Light primer strikes - fail to fire

[1075 tech]

I put together a build for a friend of mine. Group buy barrel and bolt. I used a Rise Armament 140 Super Sporting Trigger. Single stage 3.5 lb.

Getting some light primer strikes. This has become worse with the cold weather. I swapped out the trigger with another of the same that has worked flawlessly in one of my builds.

Still getting light strikes.

I'm going to pull and swap out the firing pin next. And maybe the bolt.

Anything else I should think about? Anything in particular I should look at?

Initially, I was thinking about maybe a bad trigger. Now I'm wonder if there is a small burr on the pin or in the bolt.

Toolcraft bolt carrier, I believe. I'll have to check.

Thanks

[grayfox]

New and stiff bc/bolt/gas rings, or maybe if you used any lube, slowing it down?
how many rounds downrange? I would try to get 50 factory rounds downrange then look at it.

O yeah, measure that FP before simply swapping. Are you using the toolcraft bolt?
Toolcraft was (and maybe still is) using a shorter fp by ~0.11 in its bcg's, so putting in a milspec fp could lead to pierced primers w/ their bolt. Has to do with how they made the bolt to accommodate the deeper face depth, they didn't add the +0.11 onto the rear of the bolt like it should be (the real Grendel bolt has the 0.136 face depth and the longer tailpiece so you can still use a milspec firing pin).

[VASCAR2]

[1075 tech]

When I get it from him, I'll check those dimensions. I used a group buy bolt. The bolt carrier, I believe, was toolcraft.

[imaguy3]

When I get it from him, I'll check those dimensions. I used a group buy bolt. The bolt carrier, I believe, was toolcraft.

The carrier shouldn't matter. I also used a group buy bolt and a milspec firing pin without issues. The above post by Vascar is great info!

[VASCAR2]

I missed that the Op mentioned using a Monster Group Buy bolt which have been very consistent with good QC. It is still possible either the firing pin or bolt/FP are out of spec. When a failure to fire occurs with two different FCG makes you think there is a possible problem with the BCG that might have something out of spec. At least worth checking to eliminate one possible culprit.

[Mad Charlie]

Check primer seating depth and headspace.

[1075 tech]

Ok. I checked bolt (from first 2018 group buy). Overall length is 2.814. Bolt recess is .134 instead of .136. Within tolerances?

Firing pin length is 3.278 and I have pin protrusion of .0305.

Upon disassembly, I found an excessive amount of oil and carbon. I would like to think this, combined with the below freezing temperatures, slowed it down enough to not ignite the primer.

But that doesn't explain the 2 misfires during the initial function testing in late summer. However, I believe they were early on with a very low round count and these group buy bolts are tight in the carrier.

Any other thoughts?

BTW, all factory ammo. Inthinknthe initial two were with Wolf steel case. The others more recently were with Federal Fusion.

[Popeye212]

I had an issue with a Rise 140 I sent it back and they sent me a new haven't had anymore light strikes. Just my experience I swapped it out with Larue MBT and put in my Sport .223

[grayfox]

Upon disassembly, I found an excessive amount of oil and carbon. I would like to think this, combined with the below freezing temperatures, slowed it down enough to not ignite the primer.

Any other thoughts?

Only other thing that comes to my mind is -- and this is from a different rifle, bolt-action not grendel -- this other 7-08 had a titanium firing pin, lawyer-like to lessen slam/srop fires, instead of steel. That, combined with low temps and some oil (Rem oil in fact) in/around the bolt/FP, led to 4 light-strike nonfires in a row while I was on stand with a deer in my sights. I think all AR FP's are stainless so probably not an issue here, but it does illustrate how a firing pin can be slowed down to give light-strikes.
btw, I ditched (traded in) that rifle and went with another mfr, with steel FPs I could trust.

[VASCAR2]

Ok. I checked bolt (from first 2018 group buy). Overall length is 2.814. Bolt recess is .134 instead of .136. Within tolerances?

Firing pin length is 3.278 and I have pin protrusion of .0305.

Upon disassembly, I found an excessive amount of oil and carbon. I would like to think this, combined with the below freezing temperatures, slowed it down enough to not ignite the primer.

But that doesn't explain the 2 misfires during the initial function testing in late summer. However, I believe they were early on with a very low round count and these group buy bolts are tight in the carrier.

Any other thoughts?

BTW, all factory ammo. Inthinknthe initial two were with Wolf steel case. The others more recently were with Federal Fusion.

I think your bolt face depth, bolt overall length and firing pin are gtg. Only other thing is if you had excessive head space but I would be surprised if that was the issue. You could measure your spent brass to see if there is excessive growth after being fired this barrel. I suspect you have an issue with the Rise Arm. trigger. Have you got access to a different lower with different type of trigger to test the upper.

[1075 tech]

I think your bolt face depth, bolt overall length and firing pin are gtg. Only other thing is if you had excessive head space but I would be surprised if that was the issue. You could measure your spent brass to see if there is excessive growth after being fired this barrel. I suspect you have an issue with the Rise Arm. trigger. Have you got access to a different lower with different type of trigger to test the upper.

Didn't measure, but fired brass looked fine. I did swap out the trigger with one that was proven to work in another lower. The same brand.

Now that I've cleaned the bcg thoroughly, we'll give it another go. I'll let you know.

[FRB6.5]

Assuming pin protrusion is within spec I'd suspect either lubricant thickening or carbon build up within with the bolt causing excess drag.

If the ammo was Hornady American Gunner, I've also experienced missing anvil in primer like another poster has.