Stuck rounds in .308 Semi Auto

[tfosters01]

I took my new build to the range for the first time today and fired 40 rounds at 100 yards. It grouped well for the start of the break in period(.75 MOA) but I had 4 rounds where the BCG did not close all the way and had miss fires. I am reloading but have full length sized all of the brass with new dies. The upper is a DPMS 24" fluted bull barrel. Are there any sugestions on a fix to this intermitant problem?

 

[Buffalobob]

One possibility is to go to small base dies. You can tell if that is the problem by cycling your rounds through without firing and see if some of them always stick and hold the bolt open. If the same pieces stick each time then you have a trail to start following.


Second possibility is to take it apart and clean any storage grease off of it. Pay close attention to the spring and buffer group especially the inside of the tube and spring. Degrease it entirely and then try a spray on dry lube. Guess how I spent yesterday afternoon- Browning jam-o-matic shotgun - and the incredible thing is that Browning knows full well that within a couple of years their grease hardens up and will not allow the recoil spring to function properly.

 

[tfosters01]

Thanks for the input. I have not heard of small base dies. Who sells them? Are they the "Bench Rest Dies"?

 

[Kevin Thomas]

If I'm following correctly, the brass was fired in another gun, and then resized and fired in the DPMS? If so, then that's likely the problem, and the Small Base Dies Bob recommended should cure the sticking. You might want to use these as your standard dies for this rifles anyway from this point on. Many folks aren't aware of this, but full length sizing in most makes of dies do not return brass to its original, unfired dimensions. Small Base Dies are simply of somewhat tighter dimensions than regular full length dies, and will bring brass back to nearly its original unfired measurments. I'd suggest starting with new brass for this combination, and using the Small Base Dies from this point forward. Most makers offer these types of dies, so just double check that that's what you're getting when you order. Another item that I'd very strongly recommend is a chamber gage or other type of headspace gage so that you can measure just how much you're bumping the shoulder when you set up your dies.

Reloading for semi-autos is a bit different from what you might be used to with a bolt guns, and it needs to be approached from a very different perspective. Forget anything you know about benchrest reloading, and a good bit of what you know about reloading for bolt guns in general.

Hope this helps,

Kevin Thomas
Lapua USA

 

[tfosters01]

Very helpful information. I have a sent of smaal base dies coming in the mail now. Thanks for the help!