light primer strikes on my 6.5 Grendel, not the lower...

[zghorner]

Went shooting yesterday and had 2 or 3 light primer strikes out of 60 rounds fired. All factory Hornady ammo. I use the same lower for a 5.56 AR shooting mostly cheapo steal case and never have a hiccup. I know the hammer spring is on correctly and I just don't really suspect the lower to be the problem.

The upper was bought complete from a friend and has only had (less than) 300 rounds through it. I have had issues since I got it with FTE and now the light strikes. I added an O-ring to the extractor spring as well as an adjustable gas block and now it is running much much better.

WHAT EXACTLY IS HAPPENING: pull the trigger -> click (round did not fire) -> rack the bolt -> ROUND DOES NOT COME OUT -> if I pull the trigger again it will shoot like normal operation -> If I rack it again instead of pulling the trigger it will pull out the unfired round with a small depression where the firing pin struck it.

A few things to note, the bolt is pretty abrasive while moving/rotating in the bolt carrier. The carrier looks to be chrome to me and has some poor machining inside where the bolt is. I smoothed it up with some lapping compound but it still is sub par IMO...that carrier is hard stuff.

What I think is happening is the bolt is not going into full battery but I am no expert obviously. Where should I go from here to solve this issue? extractor too stiff? recoil spring too weak? I'm running a rifle buffer setup with new spring.

thanks in advance for any advice.

 

[mr ed]

Is this on the first round loaded or middle of the mag? closing bolt by pushing bolt catch or lowering by releasing charging handle?
is the brass scored by the extractor? (spring and o-ring too tight)
since it uses a 7.62x39 bolt head I would look for a burr in the firing pin hole. use a Q-tip and spin it down in the bottom of the hole.
if it tears some of the Q-tip then theres a burr. I would check firing pin protrusion with a depth mic or dial caliper.
might look into the "improved" firing pins for 7.62x39 bolt heads. my first bolt heads I used 223 bolt heads opened up to correct dia.
back in 1985 and never had a problem. last year I built my daughter a 7.62x39 bought a new commercial bolt head and had to buy a new FP as the mil-spec one didn't stick out far enough.

 

[zghorner]

Is this on the first round loaded or middle of the mag?

middle of the mag

closing bolt by pushing bolt catch or lowering by releasing charging handle?.

abswered above, since it is middle of the mag it normal recoiled operation of the bolt. Then after the light strike I rack it with the CH and it catches the round. Also last round BHO functions correctly, I have tuned a fair amount of gas blocks and it is not running on the ragged edge.

is the brass scored by the extractor? (spring and o-ring too tight).

It was scoring the brass badly but I removed the fangs from the extractor when adding the o-ring. now you can see small impressions from the extractor but they don't look very bad (again, not experienced enough to say how much is acceptable). Pics attached although they aren't the best.

since it uses a 7.62x39 bolt head I would look for a burr in the firing pin hole. use a Q-tip and spin it down in the bottom of the hole.
if it tears some of the Q-tip then theres a burr. I would check firing pin protrusion with a depth mic or dial caliper.
might look into the "improved" firing pins for 7.62x39 bolt heads. my first bolt heads I used 223 bolt heads opened up to correct dia.
back in 1985 and never had a problem. last year I built my daughter a 7.62x39 bought a new commercial bolt head and had to buy a new FP as the mil-spec one didn't stick out far enough.

thanks for this I will check it out.

[/QUOTE]

 

[MrShooter]

I'm betting you have the hammer on the right

 

[zghorner]

yes, but it has been bobbed due to me replacing the factory springs with jp yellow.

 

[O4L]

It sounds like the bolt isn't closing completely for whatever reason.

 

[mouthpiece]

Try a regular hammer spring.
Very common for JP hammer springs to not be strong enough to set off some primers.
Then adjust from there.

 

[doctorjj]

Try a regular hammer spring.
Very common for JP hammer springs to not be strong enough to set off some primers.
Then adjust from there.

Not if the hammer has been bobbed. It's not going into battery fully.

 

[zghorner]

Not if the hammer has been bobbed. It's not going into battery fully.

yes this is my feeling as well. Plus I find it hard to believe that the same lower will ignite Russian garbage primers all day but fail to set off hornady...

I changed out the o-ring on the extractor with the recommended size, the one I had on there was no doubt too big. I wonder if the increased resistance on the extractor was preventing it from grabbing the casing lip and kept it just far enough out of battery to strike light. We will see on the next range day.

 

[mouthpiece]

What does the underside of the carrier look like? Is it the clearanced "safety" carrier that allows the notched hammer to catch FP? If it is, it may just be running slow enough to catch the FP.