Semi Automatic Bren Gun Conversion

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					               Semi Automatic Bren Gun Conversion
                  Midwest Metal Creations LLC
Thank you for your purchase of this bren gun conversion kit. It will allow you to take a demilled parts kit
and convert it into a functional semi automatic only rifle. Please note that many of the steps can be done out
of order if needs be except for the receiver build process, this must be done in exact order to remain in
compliance with federal laws. It is your responsibility to ensure that you will not be violating any state laws
in the building and use of this firearm. Also be aware that you are accepting all responsibility for the safe
use and care of the end product. Due to the age and various conditions of the used parts in the firearm,
Midwest Metal Creations LLC can accept no responsibility or liability for the end user in event of accident,
negligence, parts breakage, or intentional misuse of the completed firearm or any of its new or old parts.

 This CD is not to be copied in part or whole for any reason, or information disseminated to anyone. Only
the owner of the conversion kit or welding jig has permission to print, own a paper copy, or own this CD or
any of the data contained within. The information contained on the CD along with dimensions of the
conversion parts and welding jig dimensions and procedures are considered intellectual property and you
may not copy them in part or whole.

 First order of business is a good degreasing and inspection, some of these parts contain the most vile
grease I’ve ever seen, and it all must all be removed. Learn how to disassemble all of the major
components, this will come in handy later. There is a lot of grease hiding in these parts that will foul your
equipment when heated later in the grinding and cutting process. Inspect all parts for cracks and heavy
wear, replace if necessary. Many of these guns, now in parts kit form were retired from use because of wear
or a multitude of non serviceability reasons so don’t be surprised if some parts fit loose or there are broken
parts. Inspect the cut receiver pieces and check for bent or warped edges due to cutting or shipping.
Straighten the bent pieces as best as you can before inserting onto the jig. Inspect the firing pin hole in the
breech face, it must have crisp edges and not be eroded. A larger pitted ring around the firing pin hole
caused by primer leakage of wartime ammunition is acceptable if it does not contact the firing pin hole.

 Clean up the slag and debris from the receiver pieces. The cut edges must be made smooth on the inner
and outer surfaces so you have a clean surface to start from. Only remove the jagged edges for now, once
the receiver is on the jig you will determine what additional material must be removed. Pay attention to
squaring up the inside corners of the receiver. The roof of the rear section and under the magazine holder
lips in the magazine well must be clean and square. Clean up the inside keyways so the lower and the
internal can be inserted and move about freely in the receiver. Pay attention to the cocking lever slot, this
area is bent easily. Make sure the cocking lever can be inserted into its slot and moves freely before
proceeding with the receiver build. Once all of this is done, thoroughly clean the inside of the receiver of
debris, shavings, and grinding dust.

.094 cobalt drill bit
.125 carbide drill bit or center cutting end mill
Carbide end mills, .250, .375
Vertical belt sander
Milling machine with standard assortment of HSS end mills
Welder, Gas shielded Mig or Tig welders preferred
Combination disc/vertical belt sander, 1”or 2” preferred with changeable grinding angle
 The rest of this manual will be in two parts, the parts conversion and the receiver build. First we will start
with the parts conversion. The lower must be stripped of all major parts except for the ejection port cover
which is inop in the completed rifle and can be locked open out of the way. There must be milling of the
lower receiver to make room for the new parts, it must be a smooth, uniform surface so no rotary tools are
allowed to be used in these areas. The original disconnector must be modified by the removal of the lower
sear surface and of material on the trip surface, see modification sheet (Fig A). The pin that holds the
trigger and the disconnector must be pin pricked with an awl in 4 areas around the pin on both sides to
prevent it from working loose. Use light hammer taps as the pin is unhardened. Make sure the parts can still
rotate freely.

 Next we will mill out the lower to make room for the new components. Refer to Fig. E for the correct
measurements of the cuts to be made. The forward, .710 wide cut, will contain the hammer and its drive
spring. The .660 wide area will contain the sear, safety, and the hammer in its cocked position.

After all of the cuts inside have been made the lower is flipped over and a .375 dia. hole is drilled into the
autosear recess, see Fig. J. The autosear block is installed and welded into place through the hole. Before
welding check to make sure the sear spring base will still fit into its original recess. Once welded grind the
weld down flush, the pistol grip will cover this weld so don’t get too carried away.

Several holes must be drilled into the side of the lower receiver (Fig. H), the first .187 dia. is for the
hammer pivot pin, the .094 hole is for the sear stop, and the last .250 is for the safety. These hole are
marked from the edges of the existing holes in the lower and the top lip of the lower receiver. Drill bits of
the correct diameter inserted into the existing selector and sear pin holes using the unflutted shank section
make good edge finders as all of the existing holes are in English measurements. The holes can be drilled
from one side through but be very careful that your setup is square, it must be done on at least a drill press.
Use a quality drill bit with heavy lube oil on low speed.

The recoil rod tip is drilled using a .094 cobalt drill bit to the specified depth (Fig. F). A lathe is needed
here as a centered hole is a must. Insert the .094 roll pin fully and grind it down so .200 protrudes from the
recoil rod tip, lightly grind the sharp edge from the cut roll pin.

The firing pin is modified according to Fig G. First the OAL of the firing pin is reduced to 1.885 inches.
This is done by very carefully grinding the tip of the firing pin flat. The tip must have square edges so do
not round off the edges created, debur only lightly with a hand file. Next we put a small spot of weld inside
the retention groove of the firing pin in the area that holds it in place by the original pin, use low heat.

Grind the weld spot so it is round again and will fit into the firing pin recess in the bolt. Now we will
carefully start removing material inside the retention pin groove so when installed in the bolt and with its
retention pin inserted the firing pin tip is flush or sticking out only a few .001’s from the breech face. Install
the new firing pin spring, crimped end first.

This is a hand fitted job and must be done carefully. All of this is done to prevent primer flow. Since the
new hammer doesn’t have the mass of the bolt carrier under spring tension like any other open bolt gun, the
primer will flow into the recess around the firing pin while in the bolt. If this space is too large the primer
will rupture and eventually erode away the firing pin tip and the breech face around the firing pin recess.
We are limiting this space by taking some of the curvature out of the front of the firing pin and limiting the
rearward travel of the firing pin to just the breech face, thus preventing excessive primer flow and blow
outs. Anyone who owns an Ohio Ordnance semi BAR or a Glock pistol sees the same thing, slightly
extended primers.

 Now we will start on the bolt modifications. Refer to Fig. B for all of the measurements. The rear of the
bolt has material removed for the firing pin extension. The right side of the bolt also has .075 material
removed from an area of it because of the thicker piece of receiver that will be welded into place later.
The metal is case hardened to about 60 RC so carbide cutters are need to remove what is needed. The .250
wide cutout on the bottom of the bolt in Fig. B is also made at this point.

Now we want to fit the firing pin extension. The interior cavity of each bolt is a little different so each
extension must be fitted to its bolt. The extension will have 4 sharp corners, each one must be rounded off
on the front first and then the back by grinding so it slides around freely into the back of the bolt and
pushes the firing pin forward when fully depressed. The extension is hardened so keep it cool by frequent
quenching in water to prevent annealing.

Some rounding of the corners on the front of the extension that contacts the firing pin might be needed to
conform to the front curvature of the hammer raceway inside the bolt so the firing pin can extend fully.

The extension should spring back from the new firing pin spring when tension is released. Firing pin
protrusion should be in the .035-.040 range when the firing pin extension is fully compressed.

The recess on the bottom of the bolt is for the firing pin extension retaining block that will be welded in
place in the hammer raceway at this point. The block prevents use in open bolt configuration and also holds
the firing pin extension in place. After the cut is made, bevel the edges along the cut in the bolt and the
mating surfaces on the threaded block at 45 degrees at least .050 deep on all surfaces to be welded. This is
for proper penetration of the weld seam all along the edges. When installing the block, be sure the threaded
hole is centered in the hammer raceway, it is off center by .075 so it should be obvious. The block should
be centered and held in place by a small C clamp. Weld all along the perimeter of the block, be careful
around the threaded hole so as not to fill with weld or destroy the threads.

Grind the edges smooth once cooled and use a 120 grit sandpaper wheel or emery wheel to polish the
surfaces to match the original finish. Small touchup welds can be made at any time to fill any small voids
left after the initial grinding.

Fit the extension into the bolt and remove any amount of material on the extension that will not allow it to
fit under the threaded block that was just installed.

Insert the lathed allen head screw so the head is at least flush inside the hole. Make sure the extension is
still free to move. We now will check the gap between the tip of the firing pin extension and the back of the
firing pin. There must be a small gap here (.020 or less), so that the original pin holding the firing pin in
place will bear the force of the primer flow when a round is fired, not the lathed allen head screw.       11
Push out this pin with the extension installed and the firing pin should move back a small amount as visible
from the breech face. You should not be able to push the pin back in without pushing in a little on the
extension, if this is so you are ok. If not then remove the extension and remove a little material from the tip
of it. You shouldn’t need to remove more than .010-.015, worst case scenario. Apply a low strength thread
locker to the threads of the lathed allen head screw and reinstall.

After this effort is completed the rear of the firing pin extension must be ground for clearance for the bolt
carrier when the assembly is going forward and the ramp on the bolt carrier pops up the back of the bolt
into the locked position. Grind the rear section that faces down of the firing pin extension to a 25 degree
angle to a depth of .050, this will give adequate clearance for the extension. Once again remember that this
part is already hardened so use frequent quenching in water to keep it cool.

Assemble the firing pin extension into the bolt and the rear section of the bolt should look like this.

The bolt carrier group is next on the list. Remove the original hammer and the cocking stud on the carrier if
you haven’t already done so. We will remove the gas piston by using a .156 or smaller pin punch on the
dimpled side of the headed rivet that holds the piston in place. Punch out this rivet and unscrew the gas
piston, set aside for later. Take the original hammer and modify just the hammer area and the cocking stub
area for now (Fig D). This part will now be known as the unlocker.

When this is done do the mods to the cocking stub as shown in Fig. C.

Remove the .600 of material from the front keyways of the bolt carrier (Fig I).

Now we will drill out the recoil rod recess on the back of the bolt carrier, use a .125 dia. carbide drill or
center cutting end mill to drill a thru hole in the center of this recess. After this is done grind down flat the
small ridge around the recess to the level of the surrounding metal. (The picture shows the rear curvature of
the bolt carrier already done but do not grind this area yet.)

Reassemble the modified unlocker and cocking stub to the bolt carrier.
We will now start milling the bottom of the bolt carrier, refer to Fig I for the correct dimensions. (A note
for persons doing the mill work themselves, the modified unlocker is under spring tension and will move
about when feeding against the spring tension and chip the edges of your mill bit if you try to remove too
much at once.) Once complete round off the edges of the stub that remains on the bottom of the carrier.
This stub will activate the disconnector in the lower receiver and permit semi automatic operation.

(A partially completed mill job on the bottom of the bolt carrier)
 Once the bottom is milled disassemble and debur all of the cuts made, as they will be very sharp. Now its
time to grind the curvature on the rear of the bolt carrier, this area is what contacts the front of the hammer
and cocks it.

 Grind and polish it to roughly look like the above picture, don’t make the web of material between the
bottom and the recoil rod recess too thin or it will be prone to cracking.

 Next we will install the piston extender on the piston and screw it back into the recess. Because of the
extra power needed to run the rifle now that it has to cock a hammer we will need to have the gas act for a
longer time on the piston to get more power from it. By inserting the part into the pin retention cut on the
threaded part of the piston we can screw it back into the bolt carrier as far as it will go and reinsert the
original rivet pin. It is now held in place, unscrewed about 2 whole turns from its original position, so you
can still have use of the gas settings on the regulator.

Now that the conversion of the parts is done we will assemble the parts to the lower receiver and check for
function. First we will assemble the hammer and associated parts. Insert the hammer spring and guide
bushing as pictured. Center the bushing and tighten the locking allen screw on the bottom of the hammer to
hold in place.

Insert the spring tension bushings on each side of the hammer.
We will now insert the hammer into the recess created for it in the lower receiver and insert the headed
pivot pin through the .187 dia. hole in the lower from the left side of the lower. You won’t be able to cock
the hammer all of the way because the hammer spring legs need to be trimmed to length. Hold the hammer
at 90 degrees to the lower and take a felt tip marker and mark about .025 from the edge of the spring recess.


Cut the legs of the spring off at these marks with a rotary wheel; remember you can always trim more off
later, so don’t cut it too short. When this is done, use a vise grip to grab just the tips of the spring where
you cut them and give them a small bend inward and debur the edges. This will prevent the edges from
digging into the softer steel of the lower receiver when in use.

Reinstall into the lower receiver and try to cock the hammer, if it meets resistance from rubbing on the
sides then loosen the allen screw and recenter the hammer on the bushing by cocking it with the screw
loose. Once you find the center retighten the allen screw, we will apply permanent thread locker to it later.

Now we will install the sear assembly. Insert the long .094 roll pin through the both holes cut into the side
of the lower, trim both sides so no more than .025 of it sticks out.

Take the helper spring and intertwine it with the original sear spring until it is flush along the top with the
original spring.

Install the springs in the lower into its recess.

Install the trigger and disconnector into the lower receiver. Take the new sear and install it in place of the
original sear. Put the top of the spring in the spring recess on the underside of the sear and push down and
under so it slides under the roll pin that limits its forward travel, insert the original sear pin.

Pull the trigger and the sear will rock back, push on the top of the disconnector and it should snap back into
place, held back by the roll pin. Push the hammer back carefully and the sear should ride up and over the
sear areas on the hammer and lock into place. Remove pressure from the hammer and it should be held
back by the new sear. Reapply pressure to the hammer and pull the trigger, the sear should break from the
hammer, ride it back with your fingers to the rest position. Never let the hammer fly forward unimpeded
when testing, the sides of it will dig into the area forward of it.                22
 Once the hammer and sear is fitted and they interact properly with each other remove the hammer from the
lower. A small flat notch must be made on the bushing that goes through the hammer for the allen head
screw. Remove the allen head screw and the bushing from the hammer, inspect it for a mark left by the
screw. At that mark use a rotary tool and grind a small flat area about .010 deep. Reinstall the bushing and
apply permanent thread locker to the allen head screw and install and tighten down. Quickly install the
hammer into the lower and recheck the fit and function before the thread locker sets up.

No we will install the safety. Insert the safety spring into its recess and place the BB on top of the spring,
this will provide a detent after we drill small impressions on the floor of the lower.

Invert the lower receiver and place the safety inside the lower with the small protrusion facing forward and
line up the .250 dia. holes. Insert the .250 dia. rod through the lower receiver hole and the safety. Move the
safety as far as it will go to the right side of the lower, position the .250 rod so when tightened down you
can use it to move the safety side to side inside the lower.

Now we will need to notch the rear of the sear for the safety. Remove .160 material from the rear of the
sear, enough to allow it to pivot on its axis pin when the safety is in the fire position. 24
The above picture already has the sear notched but here is a picture of it outside of the lower in their
relative position for comparison.

Once this is done and the safety operates as it should, remove it and apply a thin coat of cheap black paint
in the area of where the spring loaded BB detent rides inside the lower. Reinstall the safety and move it
back and forth several times, enough to leave a mark in the paint of what the range of movement is on the
safety. Prick the two ends of this line with a center punch and use a .125 dia. drill bit to drill a .025 deep
divot at these two points to act as the detents for the safety so it will not move during firing.

Install all of the parts back onto the lower receiver, buttstock, pistol grip, and recoil assembly at this point
as we are finished with them for now.

Now we need to take care of that evil flash hider, after the ATF turned down the original sleeving design
for a muzzle break, a new design that had holes cut into the hider was submitted. Nothing was ever heard
about it again and I’m sure they don’t plan on doing anything with it being so close to the potential AW ban
sunset. At this point the hiders must be cut off the barrel you plan on using so as not to violate the AW ban.
Use your worst Mk II barrel for this, save your best one for when the AW ban sunsets, if it is not replaced
then you’ll be able to use regular barrels on the rifle. If the AW ban is replaced with something similar then
inquires will be made as to what happened to the previous submissions and what needs to be done to make
a legal muzzle break. So for now, cut the hider off just in front of the barrel so none of it remains, that way
you’ll be nice and legal.

If you are unable to do the above mentioned modifications for your rifle build then Midwest Metal
Creations can do it for you. The price is $250 payable by bank or postal money order to have the original
parts modified, flash hider from one barrel removed, and have the new parts installed, fitted, and tested.
They then will be return shipped to you ready to install into your semi auto receiver. The picture below is
of the items that need to be shipped to Midwest Metal for modification. Please send them clean and free of
grease and other preservatives. Please remove the buttstock and pistol grip from the lower receiver and
submit only the pictured items (No receiver pieces please as we cannot reweld or modify them for you)
along with payment and return address to:

Midwest Metal Creations LLC
1930 Hwy 6 NW
Oxford, IA. 52322        Please email in advance of any incoming work so we know it’s coming.

The list of cleaned and degreased items to send to Midwest Metal for mods along with the new semi parts
purchased from us include, stripped lower receiver(minus butt stock, pistol grip, and recoil tube), bolt
carrier(complete), bolt(complete), recoil rod(minus spring), sear spring and holder, trigger and
disconnector, sear and trigger pins, and 1 barrel to have the flash hider removed.
Part 2, Receiver Build
Additional tools needed to complete the receiver build.
4 inch C clamps, quantity 2
A sheet of aluminum foil
Non flammable shimming material if needed
.625 diameter, 12 inches long solid aluminum rod if receiver has been cut in 4 places

Please listen to this warning, it is quite serious and needs to be followed. All of the receiver build steps
must be followed in order as they appear to be in compliance with federal law so at no time will you be in
possession of an NFA controlled device.

 With the welding jig you will receive copper plates to be positioned between the weld and the jig. Also
included is a brass rod that will be used with receivers that have been cut in 4 places. It will be inserted into
the gas cylinder and be used to hold it straight and to form the inside bearing surface for the piston. The
pieces of copper fit to the jig in the following order, the sizes are approximate. Some minor trimming of the
copper might be necessary so that they do not interfere with the seating of the receiver pieces onto the jig.
The 2 .900x2.00 are for the lower portion of the front cut through the barrel nut. The 4 2.00x2.00 pieces are
for the lower portion of the cut through the magazine well and for the sides of the rear section of the
receiver. The .625x1.125 sections are for the upper portion of the barrel nut, and the 2.00x1.00 sections are
for the upper portion of the magazine well. An additional .900x2.00 piece of copper is used for the roof of
the receiver on the rear section.

You should have a clean, stripped receiver, minus its locking shoulder which is under the ejector assembly,
before attempting to insert the pieces onto the jig. We will do the initial fitting without the copper inserted.
Press the pieces carefully onto the jig, they will be tight so keep an eye out for snags inside the receiver that
must be removed. From now on the receiver pieces will be referred to as #1-#4, with the gas cylinder
section being #1. Insert #2 receiver piece onto the jig and push back until the bolt stops come to a rest
against the jig. Insert #1 and use the barrel locking nut to get proper spacing between the two pieces. Insert
#3 and push forward on the piece, towards the other two pieces, the steel square on top of the jig will fit
into the area of the locking shoulder and stop it against the ledge inside the receiver. Insert #4 and insert the
locking pin through the jig, it will be very tight so use a rubber or plastic mallet to drive it in. If the rear
section has been destroyed through the locking pin just position it with the edge of the jig, it is the correct

 You are looking for smaller than .125 gaps in the receiver when fitted to the jig. These gaps must be
widened so that proper penetration of the welding apparatus is achieved. Mark these areas so that they can
ground down after the parts are removed from the jig.

Once this is done a 45-degree bevel must be ground into the edges of all of the weld areas of at least two-
thirds of the thickness of the material that is to be welded. This is also for proper penetration of the weld
and for a stronger, void free weld seam. After grinding debur the inner surfaces and recheck the gaps by
reinstalling the parts onto the jig.

  Remove the sections and install the correct size copper plates in the jig recess, these plates will make the
fit a little snug so be patient when installing the plates and receiver pieces. You might have to trim the
copper or hit those high spots inside the receiver that you missed, the copper will rub and the offending
area will be easy to spot. Make sure the plates fit and are in place and cover all areas that need to be welded
over. The area covered by the plates is large enough to cover most cutting jobs without compromising the
jigs ability to hold the receiver sections straight. On the rear sections of copper you will have to notch the
plates for the takedown pin so it will cover the area needed to be welded and still fit in the jig and let the
take down pin being driven in place. This is done because of the wild variance in where the cut is made and
so people with Sarco cut receivers that have had the takedown pinhole cut through will have a chance to
rebuild the area.

 There are 6 aluminum hold down assemblies that are used with this jig. The threaded eyelets that come
with them need to have the open loops of the eyelet welded closed so when the hold downs are tightened
they don’t open up. Also the supplied washers must be installed on each of the eyebolts used with the hold
downs. The holes in the baseplate of the welding jig will be referred to as #1-#7, going from the front
where the tip of the receiver goes, to the rear. There are three types of aluminum hold downs, each one is
made from a 1.00x.500 piece of aluminum that is 3 inches long. 4 of them are drilled through the flat side
to give a 1 inch wide bearing surface against the receiver. 2 of them are drilled through the sides to give a
.500 inch bearing surface. One of these has a cut to fit between the magazine well of both Mk 1 and Mk II
receivers and the rear sight mounting. The other one pulls double duty by working in the #4 and the #7 thru
holes in the baseplate of the welding jig as both are never used during the same welding operation.

 Now that you’re familiar with the operation of the jig and where the various assemblies go we will start on
the actual build process. Once again, the following procedure must be done in exact order.

 The first step only involves the people with 4 cut receivers that go through the gas tube. First we must
check the inside of the gas tube. It must be deburred and prepared like the other receiver pieces. Take the
gas piston and make sure it can be inserted into the bore of both pieces. Take the brass rod and mark the
midpoint with a black permanent marker. Insert the brass rod into either piece of the receiver that offers the
most resistance. Insert almost to the black mark and fit the other piece of receiver onto the brass rod. Make
sure the black mark is visible in the open seam, that way you know the rod is centered in the gas tube.

 Install the front end on the jig and set the initial spacing from the inner bearing surface of the barrel nut to
the edge of gas tube, where the barrel gas nipple plugs into the receiver. Don’t measure to the very tip but
the rim around it. The initial measurement should be 12 inches exactly. Install the first 3 aluminum hold
downs with their eyebolts, make sure they have been welded shut or they will open up when tightened
down. Tighten the hold downs securely and begin to weld. Begin near the bottom on one side and weld to
the top, alternate to the other side, starting from the bottom and going up. Leave a small gap near the
bottom so that the welding apparatus does not touch the aluminum jig. Also do not put the welding wire or
rod directly onto the brass rod as it will leave pits that will fill with molten steel and make the rod very
difficult to remove. Flow the molten metal around the rod. Place aside to cool, when cool to the touch
finish the top weld. Place aside to cool again, the game is to put the least amount of heat into a welding
joint and its surrounding area. Shrinking will occur after welding during cool down, this will put the total
length somewhere around 11.950 inches. Remove from the jig and grind the sides of the weld flat so that it
can be placed into a vise. Now is a good time to check the tension on the brass rod and move it around a bit
to get it unstuck. Take a .625 dia. aluminum rod, available at any hardware store, and drive it down the bore
with a 3lb. hammer or similar heavy object. Once freed up return it to its relative position and place the
parts in a vise so the underside is facing up and really tighten it down. Weld the remaining gap on low heat
and do only small areas at a time and allow to cool between each pass. Any major application of heat will
cause the area to contract and the receiver tip will not be straight. Once finished, drive out the brass rod
with the aluminum rod and grind down the weld on the bottom carefully so it will lie flat when attached to
the jig for the remaining weld steps.

 The second step, (or first if you have a three cut receiver), is to weld up .600 of the keyways on the front
section of receiver. Mark a line on both sides that is .600 from the end of the keyway cut. Insert the piece
into a vise and fill both sides with weld. Remember that all of these receiver build steps must be in exact

Grind or mill down the weld so it is at least flush with the inner receiver wall so it can be inserted onto the

 Take 2 of the .900x2.00 pieces of copper and place on the jig in the 1 st set of slots cut into the jig. Do the
same with the 2.00x2.00 pieces and install them on the 2 nd set of cuts. Take the 2nd and 3rd pieces of
receiver and place them on the jig with the copper plates centered over the gaps. Push on the 2 nd piece of
receiver until the inside bolt stops come to rest on the inside ledge of the jig. On the 3rd piece, push forward
until the back of the steel part of the jig comes to rest on the inside ledge of the receiver that the locking
shoulder came to rest on. Insert the steel rods through the bottom plate of the jig and install the hold downs
as pictured. (Except the #4 strap, pointed out by the arrow, this should be the other type where it is flipped
on its side.)

 Be sure you face the # 6 hold down the correct way to fit around the magazine well and the rear site base.
A clamp has been installed on one piece of the receiver as upon inspection of the straightness of the
receiver an edge was found to bow out and not be level with its opposite side that will be welded to it. Look
down both sides of the receiver and if you find one place a clamp of the offending area. In practice it’s not
a bad idea to place one on both sides of the gap to help keep the edges from deforming while welding.
Don’t use a lot of pressure, just enough to hold the clamps in place, you don’t want them to cause
deformations by their use.

A quick word to make the welding of your bren receiver easier and come out better. Start along the outside
edge of the gap to be welded, closest to the copper plate, and work your way inward. Don’t weld on bare
copper if you can avoid it. If the plates get too hot the copper will melt and the pits and voids will fill with
steel and vise-versa. This will make an unsightly weld and make the plates hard to remove along with
making them unsalvageable. You should get 2-3 uses from the copper plates, just clean them and touch
them to a belt sander to remove the slag and debris.

 Start the weld on the bottom part of the receiver, leaving a small gap on the bottom to clear the jigs’
bottom plate. Make a weld seam about 1 inch long on both sides and place aside to cool, as pictured above.

 When the receiver is cool, place the 2.00x1.00 copper pieces inside the magwell. Place them above the
edge of the magazine holding lips so they lie flat inside the magwell. (Once the receiver is removed from
the jig later you need to rebuild the cut area of the magazine holding lips, but not while on the jig)
Insert the spacer and position it so it holds the plates in place, flush to the inside of the magwell. Some
shimming with readily available nonflammable material may be necessary to get it into place, depending on
where the cut in the magwell was made.

Start the weld from the top of the receiver and work you way down until it meets the end of you first set of
welds. Alternate as you weld, welding 1 inch on one side and then switching to the other, until you join up
with the first seam. As seen on the above picture, bowing was present and a clamp was applied to fix it.

Place aside until cool to the touch, do not remove any hold downs or clamps for any reason until cool.

Remove the hold downs and remove the receiver pieces from the jig. It will be held on very tight so be
careful. Never pry between the bottom of the receiver and the bottom plate of the jig, it will ruin your
straight edge needed to align the receiver. If needed you can pry gently between the top of the jig and the
roof of the receiver on the rear cut of the receiver. Be mindful that you need to pull straight up on the
receiver to remove it, the receiver will shrink around the steel top of the jig and the part that mates with the
bolt stop that is internal on the receiver. Remove only the piece of copper that will be under the new
sideplate, leave the others in place, either stuck to the weld or keep them to be placed back on the jig for the
next weld step.

 Now we will cut for the sideplate, using the supplied dimensions on the data sheet, mark the side of the
receiver for cutting. A vernier caliper with sharp edges does a good job of this. If the mark doesn’t show up
well then use fast drying black spray paint to coat the area and rescratch the mark. Use large dia. fiberglass
cutting wheels if using a rotary tool. Do not go past the mark scratched for the cut near the top of the
receiver. The magazine holding lips will be just above the line so avoid cutting into them. When finished
square up the corners and check the cut, the new sideplate must be able to drop into the hole that was cut.

 Now is a good time to put any stampings on the new sideplate, before any grinding or welding is done on
it. I use the stamping “BREN Mk7 SEMI AUTO”. It’s not necessary on guns built for your own use by
yourself but it might help out with an uninformed police or range officer or the Elmer Fudd next to you on
the shooting line with a nervous look and a cell phone in hand programmed for 911.

 Take the sideplate and grind a 45 degree angle on all 4 sides of one side, the stamped or side you want
facing out. Grind this angle to about .075 deep, do the same with the inner sides of the cut you made in the
receiver. This is done to provide for a solid penetrating weld if using Mig equipment.

Reinstall the receiver and the copper plates onto the welding jig (minus the one under the sideplate) and
fully seat it. Check for gaps along the bottom where the receiver meets the bottom plate of the jig. Take a
piece of tin foil cut to the length and twice the width of the sideplate and fold it in half. Trim it so it will
drop loosely into the hole cut in the receiver. This will provide a small shim so after welding in the side
plate the receiver can be removed easily from the jig.

Drop the sideplate into place and reinstall the hold downs for the receiver and tighten them down. The
receiver can still warp while welding so be sure for any large weld steps being done the hold downs are in
place and tight.
 Place two C clamps in place to hold the sideplate while welding. Place on either end using light pressure.
Start to weld the sideplate but only on the 3rd receiver piece. Place aside to cool for 10 minutes and then
finish up the weld on the 2nd receiver piece around the sideplate. Place aside to completely cool.

Once this is done remove the C clamps and weld the surrounding area, again placing aside to cool. Remove
the hold down straps and weld under these small areas as well.

Remove the receiver from the jig carefully and remove the aluminum foil from under the welded in

Reinstall the receiver, copper pieces (again minus the piece under the sideplate), and all hold down straps
and tighten them down. Insert the front receiver section onto the jig and install the hold downs for it but do
not tighten them down. Insert the barrel nut into its recess, leaving plenty of room for shims we will be
adding. Cut out a piece of aluminum foil, double the width and the same length of the supplied .008 shim.
Fold in half and place the shim in the fold. Insert this metal sandwich from top to bottom, through the
barrel axis, between the bearing surface for the barrel nut on the front section of receiver and the barrel nut
itself. The shim material should make contact with the barrel nut and receiver in two places, on the top and
the bottom of the barrel nut. Push the two pieces of receiver together loosely and tighten down the front 3
hold downs. Be mindful of the barrel nut detent, it must be fully compressed so as not to throw off the

 We will just weld just the lower section of the joint that is backed by the copper plates on the first welding
pass. On this welding joint start at the top of the copper plate and work your way down to the base plate of
the jig, again leaving a small gap on the bottom. After welding one side immediately flip over and do the
other side in the same manner. Place aside until cool to the touch.

 Remove the barrel nut and shim material, it might be very tight so use caution. Install the .625x1.125
copper pieces into the barrel nut recess and install the supplied aluminum spacer to hold the plates flush
against the wall. (Don’t forget to install the #4 hold down as I did in this picture).

 Start your weld on the top of the open seam again and work your way down to the previous weld.
Immediately flip it over and do the same to the other side. Set aside to cool completely. Once this is done
remove the spacer and the copper plates in the barrel nut recess

 Install the 2.00x2.00 copper plates for the rear section of receiver. The pieces will have to be notched for
the takedown pin if your rear section of receiver is intact in this area. Insert a .900x2.00 copper piece
(trimmed to fit if necessary) onto the top of the jig for the roof of the receiver. Be sure the copper is just
under the welding area as the copper here is used to keep the rear section of receiver straight.

If you receiver has the takedown pin area destroyed then assemble and C clamp the sections to the jig,
without the takedown pin, using the rear of the jig as an edge guide for the OAL of the receiver. Weld using
the directions below as best as the cut will permit. After completion the area must be reformed and
takedown pin redrilled. The hole is positioned 1.830 inches from the bottom of the receiver and .510 inches
from the rear. Its diameter is .3125 for reference
Install the rear section of receiver and drive the takedown pin in, it will be tight so use a plastic or rubber
mallet. Use a regular hammer only if necessary.

 Install the #7 hold down (ignore the picture, the hold down pictured should be of the other type that is on
its side) and C clamp the long section of cocking slot to hold it in place. Be sure it is flush all along the
edge of the bottom plate of the jig.

 Start to weld, starting from the bottom, about half way up the seam. Immediately flip and do the same to
the other side. Place aside to cool.

Flip again and this time starting from the top, work your way down to meet the earlier seam. Do as before
with the other side. Place aside to cool completely before proceeding. Once cool, remove the #7 hold down
and install a 4” C clamp in its place. Leave room for the final weld to be done.

Finish the weld seam and allow to cool before removing the hold downs, takedown pin, and receiver from
the jig.

 Once removed the copper plates must be removed from the interior of the receiver. Be careful not to bend
the copper too much or to tear it, they should be good for several receivers once cleaned up and flattened. If
this is not possible a new set of plates can be purchased from Midwest Metal Creations LLC for an
additional fee.

The gap in the magazine holding lips and the bottom edge of the receiver must be filled with weld so the
areas can be reshaped to the original specs. When welding the bottom of the receiver use a low heat setting
to fill in the areas, especially under the barrel nut area. Applying too much heat can still cause warping so
be careful. Use low setting on the mag holding lips as well, it is easy to vaporize the thin edges requiring a
large weld spot and time consuming machining to repair.

 Next we will work on the barrel installation. Check the fit of the barrel locking nut, it should be easy to
insert and remove with minimal amount of play between the bearing surfaces. If the nut does not fit easily
into its recess than the front surface of the nut must be ground down just enough to allow it to fit. The front
surface of the nut is the side facing the tip of the receiver when installed, only remove material on this side.
Once the nut fits and freely rotates and is held in place by its detent and locking lever we can insert the
barrel and lock it in place. If the barrel fit is tight then we can fix this by taking a sanding drum on a rotary
tool and lightly grind the inside of the hole for the barrel throat.

Try to insert the barrel again, if it is still tight then darken the barrel throat over a candle with soot or spray
black paint in the area just ground and let dry. Insert the barrel so it is snug in place and then remove.
Check for soot deposits or scrapped black paint on the sides of the hole in the receiver. Grind on the
offending areas and retry the fit, don’t get too aggressive, remove only a little at a time. When finished the
barrel should almost fall out of the receiver when up-ended.

Start cleaning up the welds on the outside of the receiver. The grinding wheels for 4.5 inch angle grinders
that have many layers of sanding paper turned on their side and at an angle are about the best I’ve seen for
removal of excess material. There is less chance of digging into the side of the receiver if you slip and give
a much better finish to the eventual outer receiver surface. Be sure you pick up at least 2 wheels, 60 grit for
fast removal and a 120 for a final finish. Most of the outer surface can be ground using these wheels but
some areas must be cut using milling equipment or a steady hand with a rotary tool.

The inner surfaces must be recut so that the bolt, carrier, and lower receiver can be inserted into the
receiver. Free movement for the carrier and bolt is absolutely necessary while some resistance to the lower
receiver insertion is acceptable. Just so long as it can be removed and inserted without undue force. Pay
special attention to the cocking slot and mag dust cover. These areas must be cut carefully for free
movement of the parts. For you rotary tool uses, be sure to use the thin red wheels for these thin slots. Hope
you’ve kept all of those half used wheels, they’ll come in handy now.

Once your finished with the cleanup reassemble the gun and hand cycle the action. The safety must be off
to be able to cock the hammer. Check that the hammer is held back by the sear when the action is cycled, if
so then apply the safety and check that the trigger cannot pull the sear enough to disengage the hammer.
Disengage the safety and pull the cocking handle back to half cock. Pull the trigger and let the hammer ride
the carrier as you release the cocking handle. Do this anytime you are releasing the hammer from the
cocked position to prevent dry firing the gun. Cycle the action slowly so check for any spots where undue
force is needed to cock the hammer, polish the offending areas. Repeat this procedure several times, each
time releasing the hammer so you are cocking it when the action is cycled. Starting with the hammer in the
fired position and the safety off, pull the trigger with your left hand and hold it down. With your right pull
the cocking handle back slowly, you should hear an audible click that tells you the disconnector has
disengaged with the sear and the sear is now holding back the hammer. Release the cocking slowly but
keep the trigger held down. Verify the hammer is cocked by looking through the ejection slot. Now release
the trigger slowly and another audible click will tell you that the disconnector has now reconnected with the
sear. Uncock the hammer by the procedure practiced earlier and now we’re ready to lubricate for its first
live test fire.

Apply a light coat of gun lube inside the receiver walls of the receiver, on the inside and sides of the bolt,
and the carrier. Apply heavier grease on the bottom of the carrier and the face of the hammer. Small dabs of
grease should be placed in the sear slot of the hammer and at the disconnector/sear engagement. Cock the
hammer and reassemble the lower to the upper. Release the hammer spring tension if being put aside for
storage.                                               44
Rifle function and operation
 This rifle functions just like any other gas operated firearm out there today. Something to remember is to
keep the chamber clean, smooth operation and ease of extraction depend on it. Most procedures printed in
the British army tech manuals on this CD toward the bren gun apply to this gun with a few notable

 When reassembling the firearm make sure that the recoil rod tip is inserted into the hole drilled into the
back of the bolt carrier. This can be inspected through the ejection slot in the lower receiver when fully

The ejection port cover is non functional in this firearm so lock it in the open position to prevent

 The hammer must be in the cocked position before assembling the lower receiver to the upper. When
completed bring the hammer to the fired position as practiced earlier to prevent any undue fatigue on the
hammer spring during storage.

 Avoid old surplus ammunition if possible. Along with being very corrosive, which is laborious to clean out
of a gas operated gun, most have very hard or insensitive primers that might not reliably work. At the very
least buy it in small amounts to determine the reliability in this firearm. A good example would be 60’s era
South African in 5 round enfield stripper clips in bandoleers. They have very hard primers that might not
reliably work. Surplus ammo that is in boxes and were intended for machine gun use such as 80’s era South
African and 70’s Greek ammo work excellent and have the benefit of being non-corrosive. All brands of
current factory ammunition will work well. Handloads can also be used as long as you crimp the bullets in
the case and start with a middle of the road charge to start out with. I personally use surplus .308 dia.
bullets in my reloads to save money, I notice no appreciable lose in accuracy or functioning reliability.
Just be sure you use .308 sizing balls in your die if you go this route.

 With the barrel pointing downrange, begin test firing using one round at a time without the magazine and
the gas setting on the number three position. Make sure the safety is off as the hammer cannot be cocked
with it on. Insert one round manually and fire downrange, keeping your fingers away from the ejection
port. Keep an eye on the ejection port for the velocity of the spent cartridge. It should spit out with some
authority but the felt recoil should be relatively mild. Examine the spent cartridge once cool and look at the
spent primer. It should look something like the picture below with the center dimpled back out to conform
to the breech face and the firing pin in its rest position.

This is normal, this is caused by the large primer hole in the breech face. Unlike the original design which
had the mass of the bolt and carrier to hold it in the new design only has the relative light mass of the
hammer and its spring to contain the expanding primer.

 Retry the above procedure several times to check for any potential problems. If the brass is spit out with a
lot of force then you might want to try and move the gas setting to the #2 hole setting on the gas regulator.
Fire single feed several times and check for positive ejection. If it short strokes and rams the spent case
back into the chamber a lot of force on the cocking handle will be needed to remove it. Always use a gas
setting that achieves reliable functioning, it’s no fun to have to remove that stuck case. You should almost
never have to go to the #4 gas setting except for a few instances. Some causes that would make you go that
high to function the gun would be:

Excessive fouling.

Worn gas cylinder, causing much leaking around the gas nipple on the barrel. This is a major reason why
old brens were taken out of service and may have ended up in parts kit form. The only remedy for this is to
shoot on the #4 setting or replace the gas cylinder tip. Be mindful that some are screwed and other pressed
in place, both of them are pinned in place to prevent the cylinders from backing out.

Forgetting to install the gas piston extender in the bolt carrier.

Weak ammunition is not included on this list because of any major manufacturers ammunition would have
to meet certain velocity and performance specs that would not cause a failure to function. On the other hand
certain brands might cause you to have to switch the settings on the regulator between the #2 and #3
settings. Pay attention to this when switching brands of ammunition and try out a few rounds single feed so
you’re sure the gas setting is set right.

 Once it is functioning reliability, load up a magazine with 10 rounds. Make sure the safety is off, and fire
the ten rounds. Again check the primers on the spent cases to check for excessive primer flow. If the primer
is bulged out significantly almost to the point of rupturing the primer, stop firing immediately. The firing
pin must have the area built up by weld retouched up so as to fix the problem.               46
 If all checks out then you can load up a full magazine to fire, load no more than 27 rounds per magazine.
After your first outing do a complete inspection of the rifle and components. You will see a slight
mushrooming of the ledge inside the lower receiver where the hammer impacts the area when cocked
during firing. This is acceptable and will stop after repeated firing sessions.

 Check the set screw on the bottom of the hammer for tightness, reapply more permanent thread locker if
necessary. Cleaning of the rifle is done according to the British army tech manual included on this CD and
disassembly is done in reverse of the assembly instructions. Just remember that hammer needs to be cocked
and the recoil rod tip must be placed in the appropriate recess at the back of the bolt carrier for proper
assembly. Also always remember not to dry fire the rifle or leave the hammer cocked for extended periods
using the decocking procedure we practiced earlier.

Have fun and if any questions arise you can send an email to and we will try
to answer as best as we can. Please refer to the diagram or page number and paragraph when submitting
build questions.

Thank you again,
Midwest metal Creations LLC


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