Bren 7.92 Question - Caliber conversion?

[Grasshopper]

Hi,

 

New kid question.

 

Looking to add an 7.92mm Bren to the collection. Can the 7.92 Bren be converted to 303 via mag/bolt/barrel change?

 

Otherwise, anyone out there that can plug the breach and rebore a 303 to 8mm that has done this before?

 

I ask as 8mm barrels are rather made from unubtainum.

 

308 barrels?

 

TIA,

 

Grasshopper

 

ps. Answered some my own question with google fu. It seems Black River Militia covered much of this back in 2006 on another board about converting 303 barrels to 7.92. Thanks.

Edited April 10, 2016 by Grasshopper

[warren]

The answer to your question is both a yes and a no.

The 7.92 Bren was not a conversion of the .303 but a complete re-design.

HOWEVER, some .303 Brens will operate with a bolt and a barrel but the magazine is the fly in the ointment.

The Bulgarian 7.92 x56R mags can be fitted to the 7.92 Bren NORMALLY taking care of the mag problem.

I have had shot out .303 barrels re-barreled to 7.92 as a spare for my factory original 7.92 Inglis Bren, however I''d recommend using a new barrel if you go this route.

The used barrels get hard spots in them from overheating and are hard on cutters and drills. Your barrel maker will either love or hate you. Take a new barrel for conversion.

It is mostly a matter of trial and error if you are looking at a straight conversion.

Ran into the same thing with 7.62 x 51 conversions and a 7.62 x 39 Chinese Mk.II Bren conversion..some work and some do not.

Do you have a supply of headspacing shoulders as well.

I seem to think you are looking for a drop in conversion that you can swap back and forth at the range depending on what ammo you have and I wish you luck with that conversion.

You might get lucky and have one that works with total reliability but you are really pressing the cloth there.

Pick up a copy of the Bren Gun Saga (second edition) by Dugelby and you will see the difference in the components.

[Grasshopper]

Thanks Warren,

 

The 7.92 Bren I'm looking to add to the collection only has a 308 set-up. Making a 7.92 barrel out of a new 303 barrel seems like the way to go for relatively straight forward replacement barrels. I've been told ZB26 mags will work in the current configuration.

 

I am familiar with the headspacing shoulders but I don't have spares yet as this is my first Bren.

 

Thanks again,

 

Grasshopper

[warren]

Before we get too far into this: what do you have now ???

And are you looking for a drop in conversion?

If you have a L4 Bren it makes a difference, as it does with a .303 or 7.92 Bren or if lucky enough to have one of the Formosa 30-06 Brens

The different Bren calibres were not a straight conversion but actually a different set of spec's inside.

The only Bren that was a jury rig conversion was the Chinese 7.62 x 39 conversion of the Canadian 7.92 Bren and they had to modify the piston post assembly and the sear bents due to the reduced gas volume of the cartridge. In the Bren Gun Saga (2nd Ed.) all this is laid out in detailed photographs along with the magazine adapter and ejector assembly.

ZB 26 mags will work with the Canadian 7.92 Bren...UNLESS the mags are early eastern European manufacture mags.

Then they are about 2mm short and current 7.92 ammo will not fit. Not nice to find out when you are at the range.... :-(##

Am I correct is assuming you have a .303 Mk.X Bren set up in 7.62 x 51

Just be sure you get a decent barrel for re-rifling and there is no evidence of hot spots on the outside.

[Black River Militaria CII]

With all due respect, a couple observations:

 

>HOWEVER, some .303 Brens will work with a bolt and a barrel.<

 

An Inglis 7.92 barrel will fit into a .303 Bren receiver, the locking collar will lock up, and the bolt and carrier will assemble to the receiver, but the 7.92 bolt will not go into battery.

A .303 barrel, bolt and carrier will go into the 7.92 receiver and lock up but the bolt lockup specs must be checked carefully to insure that headspace is correct if one attempts to fire .303. Of course, the 7.92 magwell will not accept .303 mags nor will the 7.92 mags function using .303. A 7.92 mag could be altered to feed the rimmed .303 round, but why bother.......

You have a .308 conversion, so converting a 7.92 receiver to handle .303 seems a waste of time and parts.

 

>The Bulgarian 7.92x56r mags can be fitted to the 7.92 Bren NORMALLY taking care of the problem.<

 

The Bulgarian ZB39s are in 8x56mmR, not 7.92x56r, which has a .329" slug, not a .323" slug and a heavily tapered case with a rim so the mags are way too fat to fit into the magwell of the 7.92 receivers. I suspect you meant to say that these mags will fit the .303 receiver magwell which they will just do.

A 7.92 mag is only very slightly too long to lock up in a .303 magwell, but careful modification of the front end of the mag will shorten the mag enough to allow it to lock up in the .303 magwell.

These observations are from personal experience with .303, 7.92 Brens and ZB39 guns in my collection.

Hope this helps......

[Grasshopper]

Thanks Warren and Bob,

 

It is an Inglis 7.92 gun currently in .308 I'm adding to my collection. The desire was to find available spares in the way of barrels/magazines/bolts that could be used in the gun.

 

Sounds like my best barrel option may be a re-bore/rifle of a Mk1 or Mk2 303 barrel to 7.92 (8mm Mauser). Mk4 barrels may work but do not seem to be available either. I realize headspacing will likely be necessary.

 

From what I know, factory 7.92 Inglis barrels are not to be found. ZB26 magazines should (?) work in the Inglis 7.92 Bren. Mark 4 308 bolts and extractors fit (?).

 

Is that about right?

 

Grasshopper

[warren]

A couple of boobo's in my note that bob picked up.

The Bulgarian mags are of course 8 x 56R as to the best of my knowledge there is no 7,92 x 56R or the "r" in a LMG. Rifle yes but not LMG

As to locking up, this is the reason I asked if you had a supply of locking shoulders as you would be modifying those for sure. Length and angle.

The locking lugs are not that hard to find. I have a shit load of them, but the screw is the hard part to find.

The screw is staked in, hard to get out and sometimes you will bugger the threads removing it.

The Bulgarian mags will fit the .303 Bren...with minor modification..sometimes they do fit and other times not.

The one thing I will say about the ZB 26 mags: be careful on them. There are two lengths of followers and inside dimensions. The early mags will not work with WW II and post WW II ammo. I got caught on this one and was not aware of it as was anyone else. Not nice when you are on the range and no other mags available.

Don't cheap out on a barrel when looking for one to rebore. Get the best you can and hand pick looking for hot spots. Your barrel man will thank you and not want to throttle you.

If you have a Canadian Inglis 7.92 Bren converted to 7.62 x51 I also question why you would want to change the calibre. 7.62 x 51 and 8 mm is a lot easier and cheaper than .303

Just get a spare barrel made and enjoy.

My Inglis Mk. II 7.92 Bren was unfired when I got it .

It was one of the ones left in the Inglis factory vaults then sold off to the public in the early 60's.

[Black River Militaria CII]

A few more tips. If you have a .308 bolt, it will function fine for 7.92 if you sleeve a .303 barrel for that caliber, as they are identical to the 7.92 bolts, Your gun will probably have a 7.92 bolt in it.

A .303 barrel has a slightly longer reduced OD breech end than the 7.92 barrel so the bolt will not rise into lock onto a .303 breech end.

A simple way to observe the required lockup specification of the bolt is to remove the lower and the bolt carrier and bolt. Turn the receiver over so it is upside down and you can see into it. Take the bolt and place it upside down in the receiver so it is in its normal operating position and slide it forward into lockup against your .308 barrel. Observe how far it drops into lockup and using your fingers try to move the bolt back and forth to see if there is play between the locking shoulder and the breech face. It should have no movement or have very slight play, although I do not know the factory specs. Warren might have these specs. If you look at the upper rear edge of the bolt at the back end you will see a distinct color difference between the area that is in contact with the locking lug in the receiver and the area below it that does not contact the lug. Later, when you headspace your new 7.92 barrel remember this contact area as it indicates when the lock is fully engaged when headspaiing the new barrel.

Before chambering the 7.92 sleeve, assemble the new barrel to the receiver and lock it in with the barrel lock. Turn it upside down and slide the 7.92 bolt into the receiver as noted above, and move it into battery. It will not drop into lock since the breech end of the .303 is too long. Measure the approximate distance that the bolt must move forward to drop into lock up, which is the approximate measurement of metal that must be removed from the breech face. Don't estimate this measurement too long because you don't want to remove too much metal from the breech face or the lockup will be loose. Remove less than what appears to need to be removed and test the bolt in the upside down receiver again,, making sure that the barrel is properly locked in place, and reassess the measurement of metal that needs to be removed again. Remove a bit more of the breech face and retest. At some point the bolt will start to drop into lockup. Proceed very carefully and slowly here removing only very small amounts of breech face until the bolt drops fully into lockup. At this point the line of the contact area will be fully in contact with the lug. Also, the bolt should have no play back and forth while in Iock up.

Once the lockup dimension is correct then proceed to chamber the sleeved barrel. The sleeve of the new barrel will have the bore running to the breech face, and the reamer will enter the bore for cuttin the new chamber. Chuck it up in a lathe and start reaming out a new 7.92 chamber until you estimate that you are close to the correct headspace. You can measure the protrusion of the .308 round in your good barrel to have a reference for how far out of the breech the base of the case extends for correct headspace. Chuck up the barrel continue to ream out the chamber, going very slowly as you approach the rough estimate of case head protrusion. Remove the barrel, clean the chamber carefully and insert a dummy 7.92, made from a new round.mTap the edge of the rim with a light leather or plastic hammer to fully seat the round. Measure the protrusion, making sure it is fully seated in the chamber at the shoulder. When you are close to the correct protrusion, clean out the chamber with care, remove the extractor from the bolt, assemble the new barrel to the upside down receiver, slide the bolt in and move it into battery against the chambered dummy round. The bolt will not go into battery because the base of the case will still be sticking out too far. Measure the remaining distance that is needed for the chamber to be deepened for the lock to fall into lockup, but do not over estimate. Ream the chamber very slightly and retest, repeating this set of steps frequently until the lock starts to drop into lockup. At some point the bolt will move into full lockup. I tend to make the headspace slightly tight to insure that the cartridge is fully pressed into the boltface. By this time you will be able to tell when the bolt is almost fully into lockup, and assess how much further the chamber should be reamed. This is a judgement call, but keep in mind that it is imperative that the bolt be FULLY in lockup with the bolt fully in battery when ignition occurs. When the bolt is very slightly out of lockup and you press on it and it goes into full lockup you are in the range of correct.

Assemble the extractor to the bolt and slide the bolt into the upside down receiver and observe the action of the extractor in the breech face cut out for it. You may have to recontour the extractor cutout in the breech slightly. Put a dummy round into the chamber and teest the extractor for function and observe if it closes fully on the rim of the round and grips it correctly.

Test the headspace and ignition by pulling a slug from a new round, emptying the powder, inserting the empty case into the chamber and firing it outside. Primers can be loud. The primer should exhibit a nice deep firing pin indentation.

Live fire test at a range with one round initially, chambered by hand and fired. If it is determined that everything is correct then load a mag and fire a burst.

Hope this helps.

[Grasshopper]

Dear Warren & Bob,

 

Wow! A tutorial on how to get things done. I have not met Warren but I know Bob does this to put food on the table. Thanks to all for the help.

 

Sincerely,

 

Grasshopper

[warren]

Excellent Bob...That would have taken me a week to two finger type!!!!!

I'll see if I have the headspace spec's in my huge pile of files and documents.

Not sure how readily available the headspace shoulders are in the USA but make sure you have some and you will bugger a few in the process. They are tough material.

Again, the screw is the hard part to find.

[Black River Militaria CII]

The procedure I outlined above for barrel lockup actually will prevent the need for adjusting the lock up lug in the receiver, if the procedure is done carefully. Dealing with the lug is not easy and since you are planning on sleeving a barrel, the breech extension will be too long when it is done. Reducing the length of the breech extension carefully will allow you to set the lockup specifications without having to modify the lug.

Warre: if you read this let me know if you find the lockup specs........

Edited April 16, 2016 by Black River Militaria CII

[ar15usa]

 

Grasshopper, are you still buying that Bren?

 

[Grasshopper]

Hi,

 

In the end I passed on the 7.92 Bren. Absolutely excellent/new condition. For sure very rare. Just was not what I was looking for. Hated to pass on it but I've only got so much trigger time left.

 

Grasshopper