Bren Mk 2 Recoil Spring Issues

[djandj]

Greetings all. Question for the collective oracle. I have a 1942 Bren MK 2 (1942) rebuilt by Len Savage himself. It is chambered in 54R. Has had many issues with the main spring. His rebuild seems to use only one 3/4 in diameter sized recoil spring. When I get them from Len, they start out at about 12 inches however, after only a few hundred rounds they get crushed down to about 9 inches. I start having issues with light primer strikes and/or the trigger not resetting. I have also had issues with a couple of rounds going off with the same pull of the trigger. I am quite sure the springs he is using are too weak for the recoil on the gun. (even though I have the gas setting set at their lightest)

Does anyone else have a MK2 in 54R? I have seen other builds using two mainsprings (larger one and then a smaller one right over the metal guide rod jutting out from the butt and trigger assembly. Any ideas? Does anyone have a source for stronger springs? Ideas as to what might cause more than one round to fire at a time?

I have e-mailed Len a few times on this and he did send me more main springs, but I just keep replacing them and having the same problems.

Thanks,

Information

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[Peter Laidler]

Just from the metallurgical point of view, then this is definately(?) a spring problem. No 'spring' that is made from the correct steel wire that is correctly treated should compress from 12" long to 9" long after however many cycles you state. While we don't know the mechanical complexities of your gun, this doesn't alter the facts

As a matter of fact, I have seen a recovered Bren gun found buried on an old wartime landing ground just off the Salisbury Plain training area together with several full magazines with retuen springs that were still in serviceable, albeit not perfect, condition. The magazine springs sprung out of the base oif the magazine STILL under tension when the rust was scraped away.

Metallurgists out there comment please..... JM?

[Joe H]

djandj,

The original MkI's had a single spring. They were replaced with the double spring. Later replacement springs for both the MKI & MkII were the double spring. Sounds like you have a bad spring. They should never compress that much. Light strikes may indicate a weak striker spring if the semi is striker fired.

I have a MKII I converted to 54R. It uses a striker set up. Gas settings 3 / 4. I put a 1" plug behind the return spring (double spring) so that the return spring was in full compression at the end of the stroke. The length of spring compression in the semi with a striker is about 1" short of the full stroke due to the length of the striker.


The specs for the double spring are:

Inner 90 1/2 coil Left wire dia .036" OD .358" Free length 13.2/12.8

Outer 68 coils RT wire dia. .048" OD .477" Free length 13.2/12.8


You can buy them here:

50: SPRING, return, Mk 1 - BRP CORP Store

BREN recoil spring

Joe

[Peter Laidler]

I don't think he is using the real Bren spring/springs Joe H as they rarely give trouble or compress with age. But.....

Just to clear up a bit of doubt here forumers......
The reason for the double return spring was to buffer the rearward action of the breech block and piston/piston post assembly during its rearward travel. and NOT to increase the loading of the forward action of the working parts. This was because they had recently opened up the gas port of the Mk1 barrel to make it a Mk1* and also the gas regulator holes to suit. When they did this, all sorts of problems arose........ It was chaos! Now, the piston post hit the unlocking cam with such brute force that it 'bottomed-out- the piston post plunger inside the piston extension, spreading it out and making it impossible to remove from the piston post plunger spring - which also broke regularly due to it now becoming coil-bound on the damaged plunger*! After this, the breech block hit the rear gun buffer plate with such force that it cracked/broke the plate away from the collar at the rear. Anyway, to cure all of this the double springs were introduced. You'll realise that the poundage required to START the rearwards motion is similar with one or two springs but thereafter it starts to show as it buffers. It obviously works because cracked buffer plates aren't a real problem. But that is why Armourers always polish them so that you can see any hairline fractures that are about to get worse.

* The breaking of the piston post spring problem was never really cured but was lessened with the introduction of the different length piston post plunger and adjustment of the depth of the seating in the piston post housing. Yes, that's why there are Mk2 variants of each! The broken piston post spring became a 'user' maintenance item and as such a spare was always in the spare parts tin.

Not a lot of people know that!

[Joe H]

I don't think he is using the real Bren spring/springs Joe H as they rarely give trouble or compress with age. But.....

* The broken piston post spring became a 'user' maintenance item and as such a spare was always in the spare parts tin.

Not a lot of people know that!

Peter,

Definitely not original Bren springs. Maybe they were wound using the wrong grade of wire.

Very interesting info. I wondered why a heavy spring like the piston post spring would be in the spare parts tin for user replacement.

Joe

[Brian Dick]

See if you can get some good springs from Wolff Gunsprings. They won't steer you wrong.

[djandj]

djandj,

The original MkI's had a single spring. They were replaced with the double spring. Later replacement springs for both the MKI & MkII were the double spring. Sounds like you have a bad spring. They should never compress that much. Light strikes may indicate a weak striker spring if the semi is striker fired.

I have a MKII I converted to 54R. It uses a striker set up. Gas settings 3 / 4. I put a 1" plug behind the return spring (double spring) so that the return spring was in full compression at the end of the stroke. The length of spring compression in the semi with a striker is about 1" short of the full stroke due to the length of the striker.


The specs for the double spring are:

Inner 90 1/2 coil Left wire dia .036" OD .358" Free length 13.2/12.8

Outer 68 coils RT wire dia. .048" OD .477" Free length 13.2/12.8


You can buy them here:

50: SPRING, return, Mk 1 - BRP CORP Store

BREN recoil spring

Joe

Fantastic info here Joe. See I definitely think that I am missing a spring. Shouldn't the MK2 have one larger 3/4" recoil spring and then a small diameter spring right along the guide rod? I only have ONE spring back there. Where is the striker spring supposed to go? Cause I think I don't have one.

Can anyone post pics of their MK2 disassembled with the springs in place? I'm pretty sure I have only one spring back there.

[Joe H]

D,

There are two common types of semi conversion. Hammer fired which uses a hammer as part of the trigger group to fire the gun. It has no striker or striker spring. The striker fired semi uses a striker placed behind the carrier. It has a separate spring and is fired directly from the original Bren fire control group.

I don't know which type Len Savage builds. I doubt you are missing a spring. A weak return spring could cause the problems you are experiencing in either type of build.

Joe

[WallyG.]

Greetings:

I have many of Lens Brens... The Striker spring is the 3/4 inch by 12 inch spring that rides over the return rod and is immediately seen when you remove the butt group from the front/receiver. This spring is not original Bren equipment... and it has been added to the design to power the striker block forward to contact the firing pin when the trigger is puled The Original Bren recoil springs (if in fact there are two... as the kits used for these builds came with both singular MkI springs and the doubled up MkII) are contained in a tube inside of the butt stock...they load the return rod so if you can push it easily to the rear (into the butt) then this might be the first place to try and replace springs. The access point being at the rear of the butt. If your recoil springs are under powered then the bolt group is recoiling with much more force than required to reset the action and in the process is crushing the striker spring. BRP Guns in Maryland has new replacement recoil springs... or at least they did the last time I looked. Are you shooting 7.62x54r light ball or heavy ball ammo? If you are using heavy ball... I'd try some light ball and see if your new replaced spring performance is improved. Feel free to PM me if you wish to discuss in more detail.

[djandj]

Thanks again Wally. I have ordered the springs from BRP. Will I use BOTH the springs? (seems I should) May have to turn up the gas, but that is no problem. As is, I am running at the lowest setting. (higher settings crushed the springs much quicker and allowed the bolt group to slam into the butt with enough force to pop out the wooden spline!