Bren L4 / .308 build

[42rocker]

When my Wife asks, I'm blaming cal50. OK, it was on sale etc etc

I bought a ZB30J parts kit.... I'm happy to say the receiver looks better (in the pics, we shall see). The barrel is cut up too much for repair. But it should look good on the ZB30 tripod that I have. I believe that you have one also cal50.

cal50 you have done outstanding work in bring this one back!

Again, I'm telling the Wife, cal50 did it so I'm going to try.

Later 42rocker

Information

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[cal50]

When my Wife asks, I'm blaming cal50. OK, it was on sale etc etc

I bought a ZB30J parts kit.... I'm happy to say the receiver looks better (in the pics, we shall see). The barrel is cut up too much for repair. But it should look good on the ZB30 tripod that I have. I believe that you have one also cal50.

cal50 you have done outstanding work in bring this one back!

Again, I'm telling the Wife, cal50 did it so I'm going to try.

Later 42rocker

I did pick up the 3rd leg for my tripod~

[42rocker]

I love using one of those as the 3rd leg. Looks so good to me.
But, happy to say I have the 2-piece pole also.

Talk tripods later.

Enjoy the build. Builds

Later 42rocker

[42rocker]

After a little reviewing and double checking. We both have ZB30 tripods, like I thought we did. Your old tripod thread.

https://www.milsurps.com/showthread.php?t=75006

Later 42rocker

[cal50]

Fathers day , a day for working on gun stuff !

Put my bolt together with the internal transfer bar.
This L4 / 7.62 bolt thru me a little curve from the dimensions i used on my MKI & MKII bolts. Machined the thru hole from both sides with a carbide ball endmill. One side cut very nice , no issues or surprises. Flipped it over and went to put the hole thru the other side ( They have to line up for the roll pin ) and it was more exciting than I expected. New carbide end mill and it ate it in short order. Typically when you get thru the surface hardness the base material is not as hard. Well the other half of my bolt is REALLY hard all they way thru. Ended up going thru 4 or 5 other carbide end mills getting thru it.






After dropping the transfer bar in along with the firing pin and spring the firing pin was sticking out of the bolt face slightly and I was short on travel , my transfer bar was contacting the internal bolt clearance. My 7.62 bolt is slightly thicker in the front section by about .028".

I used a 5/16" carbide end mill and cut some clearance from the front of the pocket and faced off the rear of the firing pin so its flush with the bolt face.
Roll pin installed and its ready to go.

Rounded up my stainless steel tubing to make spring guides and striker tube along with some O-1 drill rod for the spring guide. Put lower frame together.
Need to cut down the piston post to remove the FA face, add clearance for the transfer bar and weld in an extension on the piston post for the disconnector.

[cal50]

Finished winding a couple new striker and recoil springs , making separator tubes and recoil spring guide. Also slotted the bottom of the striker to clear the disconnector and not drag moving forward or back.

My other MKI & MKII builds both had recoil spring tubes that were slightly out of round and I had issues with the striker spring tube dragging with the retainer "lip" on the tube. I changed the design by making the striker pusher tube a straight diameter ( no retainer lip ) and opened up the front of the Bren recoil spring tube a straight diameter , no reduced diameter to stop the striker tube. Now there is nothing to drag.

Before you had to remove the plug in the buttstock to insert the spring separator , now it goes in from the front , just drop everything in and set the striker on the sear.

Test fired a few primed cases and everything went bang. Test fire planned on the 4th.

[42rocker]

Sounds like more great work. May all go well on the 4th of July!

Thanks for sharing so much info.

Later 42rocker

[cal50]

Well I can now claim victory / I had a successful test fire and wrapped up a couple minor issues that I missed and created.



My initial test fire I thought I had it but I was getting singles , doubles then no firing. I was stumped at first but after looking closely at my parts I noticed my ignition issue.

My L4 bolt was slightly different in dimensions than my MKI & MKII builds. My firing pin was actually proud of the bolt using the same dimensions for my transfer bar.



That was an easy fix by taking a slight amount off the rear face ( impact area ) of the firing pin. I set it to flush with the bolt face thinking it would help prevent any prime flow back. I never had any flow back issues with my .303 guns and used stock bolts so I thought it was an "enhanced" thing I was doing.



This snapped primed cases and never missed a beat. Test fire day 1 I was getting one or two shots then nothing would fire.

Looking at my bolt I noticed my firing pin was now about .025" recessed back in the bolt. Turns out the harbor freight 1/8" roll pin was dead soft and bent like a "U".



Bent pin~











My fix was using a standard steel solid dowel pin and I set the firing pin recess the same as a stock Bren gun. Once again test fired several primed cases and it was 100&.

Go to the range and thinking I "got it" I was still getting some light strikes. Looking at my parts my tube that pushes the striker and rides over the other tube in the buttstock was rubbing internally. Simple spring tweak to the closed end loop and ignition is 100%



What I missed was chamfer on my barrels face to allow rounds to enter the barrel without damage or impact. The magazine is a double feed from L&R sides and the bullet nose was hitting the barrel face , not enough chamfer. The wild part was it was always on the 2nd round. One round in the mag fed and fired , 2nd round would slam the barrel face and not fully chamber. I had one round the bullet slid back into the case. It was obvious when I looked at it. The L4 barrel fitting instructions shows a barrel with a heavy chamfer all around the end of the chamber. They did this for an easy machining operation. The chamfer is only needed opposite the feed ramp area.



I got the dremel tool out and put a small chamfer that meets the feed ramps in the frame. Now it feeds smoothly by hand or under power and no bullet point damage.

Clearance is opposite the extractor clearance cut.













I need to wind a new striker spring with closed ends and pull it apart to pretty it up and park & paint it.











Proof of life and some random pics along the way~

[browningautorifle]

Very nice, good to see you too. Well done that.

[Low & Slow]

Great to see it up and running properly!