Finished a new build a couple of weeks ago.  Everything seems to be working well except for the fact that the bolt isn't locking back after firing the last round.  The only time it will lock back after the last round is shot is when I'm shooting lighter bullets such as. 55 or 60 gr.  When I'm shooting my 69 or 75 grain reloads the bolt never locks back after the last shot is fired.

Rifle is built with
Seekins upper and lower,
Shilen 20" SS Match barrel with 1 in 8 twist, Wylde chamber,  This barrel came with a matching bolt with the same serial number as the barrel.
Geissele SSA 2 stage trigger
Magpul PRS Stock
Midwest Industries hand guard
Gas port is rifle length
A2 buffer tube
Buffer 5.1 oz
Bolt carrier 9.4 oz
Buffer spring is 12.5" relaxed
All parts are new

I have about 200 rounds through the gun and it shoots  < 1" MOA.  I was hoping that the problem would go away after the rifle was broken in. However that hasn't happened yet.  I should state that I've been loading the heavier bullets with lighter powder charges so perhaps that is part of the problem. However the powder amounts are within specs.  My 55 grain and 60 Grain bullet reloads seem to cycle fine after the last shot is taken and the bolt locks open.  I've tried two different magazines and the problem persists with both of them. One is a new Magpul. The other is an older military metal magazine. Neither one works with the heavier bullets.

Any thoughts on what I should try? I thought about trying a lighter buffer or looking at other buffer springs. I removed the gas block today and everything appeared fine. I reinstalled it, ensuring that everything is well aligned but haven't yet had a chance to shoot it again.

Thanks,  Khris

Time to rebuild your reloads to function in this rifle. Get them to generate enough gas  to fully cycle the action. You may just need to shorten the bullet seating depth or add a small amount of additional powder.

If you dont want to change your load data, just accept the failure to lock open and run it like an AK platform. I would not change parts on an otherwise reliable/functioning rifle; you said it runs fine with other loads.

Given the situation you describe I would play with lighter buffers, the next lighter one should give you what you want.

This.
Tomac

Thanks for the reply.  I'll try bumping up my powder charges and see if I can get it to a point where it starts cycling correctly. I'm working on loads that I can shoot out to 600 yards so I need to stay with the heavy grain bullets.  I'm planning on shooting 75 to 77 grain bullets for the longer range shooting.

Khris

Sounds like a plan. I think I'll start with a little extra powder and see what that does and if that doesn't fix the problem then I'll find a lighter buffer. In fact I think I'll start looking for a lighter buffer right now. Never hurts to have an extra one laying around.  

Thanks.

By the way, I prefer not to be shortening my cartridge overall length (at least for now). I'm trying to make these reloads as accurate as possible and I'm trying to keep the bullet as close to the lands as possible for now.  I'm currently experimenting with a range of different cartridge lengths and eventually hope to find that one length that will be the most accurate with each specific bullet.

Khris

Follow up...

I installed the JP Enterprises JPSCS-15 Silent captured spring buffer and the problem has been solved.  The bolt is locking back every time after the last round has been fired. It works flawlessly even on those reloads that have lighter powder charges.

Khris


”The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms.” Samuel Adams

By the way the gun seems to be shooting great. I finally made it out to the range and was able to shoot out to 600 yards in a light wind.   5 shotS and .89 MOA.