L4A3 (308) completion help

[alterego]

Hello all, my first post here so please bear with me!

I have almost got my L4A3 back together and am having really only one final issue.

I do have a 7.62 marked locking shoulder installed, but the 7.62 bolt doesn't fit. A 303 bolt does fit with the 7.62 shoulder. The receiver is a hybrid of Mk I and L4A3 sections. Specifically the barrel socket area (which is the area with the bolt stops) in the receiver is Mk I.

I do not yet have a 308 barrel (waiting for Sarco or other source) so not too fired up to modify receiver before having that unless modifications are well understood.

Can anyone offer any guidance? Did the L4A3 refurbishment/conversion (from a Mk II) modify the forward bolt stops in the receiver? Kind of stumped and don't want to modify something I'll regret later.

Would be very grateful for any help in getting this old girl back up and running!

Information

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[Brit plumber]

Sounds like it was welded on the tight side. But seeing as a .303 bolt fits, you maybe able to install a shorter shoulder to get the bolt to fit. But then you need the barrel to set the CHS which means you need to adjust the shoulder if it's out.

[Peter Laidler]

To be really honest and frank, unless you have a 7.62mm barrel to be getting on with you wont really have any idea about the re-welded geometry of your very hybrid gun. Only when you get the barrel can you practically set up the gun properly as opposed to theorising. But all isn't lost. You can carefully stone the locking surface of the locking shoulder providing you don't tell anyone that we suggested it. The breech block stops weren't modified during the conversion process

[Joe H]

Aterego,

If you welded in the Mk I barrel socket into the Sarco L4 parts kit correctly the barrel stops will be in the correct location for all Brens.

To understand the difference between the .308 & .303 bolt & barrel geometry this link may be helpful (my post and answers):

https://www.milsurps.com/showthread.php?t=50218&page=9

Joe

[Peter Laidler]

Forgive me for being a tad contrary Joe, but surely, trying this before he's got a barrel will lead him up a a creek without a paddle surely?

[Joe H]

Peter,

As far as I can tell the L4 is a MK II with all the machining necessary and new ejector block to accept the 30 rd .308 (7.62 Nato)mag that was used in the FAL that GB was using at the time. The L4 like the 7.92 Bren has a different bolt and the rear end of the barrel is different from the .303 barrel. Its the combination of barrel, bolt & locking shoulder that makes each combo work and the 7.62 & 7.92 variations won't chamber a .303.

I built a semi Mk II. It will work without any mods with a .308 SA barrel and a standard .303 bolt with an L4 extractor but it probably will chamber a .303 . I though about buying one of the Sarco L4 kits and doing the same thing as Alterego but without the L4 barrel what's the use of having the L4. You can't import an L4 barrel into the US. I may get the kit if and when Sarco has usable L4 barrels available.

I would think you could weld everything up and check the weld-up with a .303 barrel, bolt and locking shoulder. If that checks out the basic receiver is ok. This will work if the forward parts of the L4 barrel such as the gas regulator are the same as the .303 barrel. It would be easy enough for Alterego to try.

The final head-spacing and fitting has to be done with the 7.62 bolt & L4 barrel. Just as you noted the locking shoulder can be shortened by stoning. I made a totally new one in one instance and TIG-ged some 4140 rod on the face of another and ground it to size successfully when i needed a longer one. The 4140 gave me a hard face to grind back.

Joe

[Peter Laidler]

Thanks for that Joe. Back here, weld-togethers are an alien concept and sometimes it's difficult to see the wood for the trees especially when the bits are hybrids anyway.

As I understand it then, you get the rear end of a Mk2 that is machined to takle the 7.62mm magazine/ejector block etc BUT you have to fit a front end to it. And you make a hybrid L4A3.

[alterego]

Thank you all for your replies! As far as I can tell (from reading other threads) there are two bumps on the rear of the 303 barrel (left and right of barrel axis), these are flush with the forward bolt stops in the receiver...whereas the 7.62 had the breechface of the barrel flush. If one were to flatten these on the barrel and match the receiver, it would look about right to fit the 7.62 bolt. I'm really not worried about the reweld, as a friend of mine helped me with it (he has done a few Brens). Peter, were these forward bolt stops modified as part of the conversion?

As far as I can tell, the modifications would prevent a 7.62 bolt from going into a 303 gun (Peter, is this correct?), while a 303 bolt would go into a 7.62 gun but just rattle around from being loose(?).

I'm not about to muck around with cutting anything on it right now, a 303 bolt does fit and seems to be in the ballpark. If I had to do anything at the moment, I'd use the 7.62 extractor in the 303 bolt.

Does anyone know the difference in length between the 303 and the 7.62 at the rearmost barrel socket diameter? Is it about 0.090"?

---------- Post added at 07:13 PM ---------- Previous post was at 07:04 PM ----------

Measuring the bolt length from the rear locking surface, the 7.62 bolt is ~0.044" longer than the 303 bolt...

[Brit plumber]

Joe, there's a few errors in your post above, the L4A3 was based upon the Mk2. The L4A1,2 & 4 were based upon the Mk3.

The A2,3,4 etc used a non NATO standard magazine as did the L1A1 rifle which would not fit a FN FAL.

If you use a 303 mid section you may run into problems with the lip for the front of the magazine as both the L4 and SA sections are modified from the .303.

Alterego, does your kit still have the circular body inserts? Last time I compared a 7.62 and 303 blocks, I found the 7.62 bolt a little longer as you found but I think Kev G posted a while back that they were the same length. I never did check again.

When I get back to the UK I can get any measurements you need. Also there are quite a few threads on this forum that discuss dimensions of the L4 guns.

[alterego]

Hey Britisher, thanks for the reply. Used the L4A3 front mag catch area. I assume by circular body inserts, you mean the circular mag supports-- yes it does. I'll have to spin some rivets on a lathe though to reinstall, unless there's a good source for them. Lovely inch FAL mags fit perfectly, as does the L4A3 mag I have. My sections split ~0.140" in front of the centerline of the barrel detent reinforcement pin so the L4A3 mag well was fully retained.

Can't wait to shoot this thing, it's my prize-pig! :-)

Doesn't look quite right without the British banana mag out the top though, will probably have to do a Mk I, just as a moral imperative.

Thank you all very much for your help!

BTW are the forward bolt stops in the receiver flat or is it a contoured/faceted surface?