AR-15 7.62x39 ftf issues

[bluto67]

I picked up a new 7.62x39 upper at the Crown Point show last week and finally got to the range saturday. First shot (Tula).. Bang. 2,3 and 4 no-go. Switch to Wolf, more failure to fire. Grabbed some Golden tiger from the range counter, first 2 went off. After that, nothing. The rounds that didn't go all had primer strikes but they may be a little light. Took the rifle apart and Dan @ Applied Ballistics and I checked everything over and things looked good. I pinned this new upper to my DPMS lower with a Timney trigger. I've never had an issue with this setup on my .223 upper. I suspect that perhaps the firing pin isn't protruding out far enough. I came to that conclusion by looking at the primer strikes and the primer seating depths. I'm not sure if there is a different firing pin for 7.62x39 setups or not. Or I could be climbing up the wrong tree. If anybody has any ideas on how to correct this I'm all ears. I'll post some pics shortly (still not very good at this stuff yet..lol).

 

[03A3]

I'm going by a vague memory, but it seems like the S&W Com Bloc caliber M&P15's have a a heavier hammer spring.
A little research might get you that info. I'm not sure how easy it would be to get that spring from S&W.
Does Wolffe (sp) make a heavier spring? Might be worth checking into.

 

[bluto67]

i plan on using a mil-spec trigger setup whenever palmetto gets off their duffs and finally sends me my new lower, but i'll look into a stronger hammer spring too. thanks


just checked brownells. extra power hammer spring stock #969-000-100. $4.99

 

[Cannon]

I had a 5.45 that did the same thing. I had to put a heavier hammer spring in it. After that I did not have any problems.