Failure to fire with AAC Ammunition

[Marvet85]

Good morning,

I have been scratching my head for a week now and have kind of hit a wall. I have a Zermatt/Big Horn TL3 SA Action in a Pork Sword Chassis build I am completing and for the life of me, I cannot get it to fire AAC ammo. It is chambered in 300 Blackout and the sole intention of this thing is to be a well-rounded garbage disposal. Here are the parts for anyone who may take the time to help me trouble shoot.

Action: Zermatt TL3-SA
Trigger: Geissele Super 700
Barrel: Black Collar Arms 9" 300BLK

Tools Used:
Zermatt Action Wrench
12pt 1-1/8 Crowfoot
Forster Go/No-Go Gauges.

Here is a picture of the build:​

The left group (FTF) of ammo is all AAC (115gr, 110gr, 125gr SMK) and the right group (Fired) is Hornady, Sabre, S&B Tactical, Winchester Super Suppressed and Ammo Inc. Not Shown is the Hornady black.​

Sorry for the huge pictures, hopefully they give an idea. Here is what I tried:

I have rebuilt the action and head-spaced about three times, each giving the same result. It does not feel tight or "forced" when closing the bolt. I believe it is head spaced right.

I have changed the trigger out to a Triggertech Special Pro from the Geissele. I have read in other posts people remedied similar issues by swapping them out due to potential drag or sear issues. No change in results.

I field stripped the bolt and cleaned the spring and firing pin to eliminate any drag from debris or thick lubricants.

My guess? The primers are hard as hell.

Question is, what can I do?

Zermatt offered to remove material to allow for up to another 10 thou in travel for the firing pin but I am not sure that will fix this. When I pull the trigger on this ammo, it's a very distinct, soft "thud". When I headspaced, the extractor was removed, so I don't think I gave myself a false head space. I am no means a bolt action expert and I am at a point of confusion as to how I can get this thing to do what I need it to do. Any input is greatly appreciated. Anyone who may figure it out, you get some coffee on me.

Steve

 

[rustyinbend]

So just to confirm ... you're saying "nothing" fires ... none of that ammo above? Or does some fire and some not?

 

[rustyinbend]

And what do you mean by ... "the primers are hard as hell"?

 

[Marvet85]

So just to confirm ... you're saying "nothing" fires ... none of that ammo above? Or does some fire and some not?

Everything on the right group is fired. Crispy break and all, the left group of ammo was that distinct soft thud I mentioned.

 

[Marvet85]

And what do you mean by ... "the primers are hard as hell"?

I didn't really capture the depth of the strike but in person you can see they are considerably more "shallow" than with the rounds that fired.

 

[rustyinbend]

Do you have the tools to measure the differences between what fires, and what doesn't? If all that's the same, and one group of ammo doesn't fire when the primer is struck, and you feel that's a problem with the primers in that lot of ammo ... then the "Captain Obvious" in me says "Don't use those primers anymore."

 

[TheOE800]

I’ll buy your Geissele

 

[Marvet85]

Do you have the tools to measure the differences between what fires, and what doesn't? If all that's the same, and one group of ammo doesn't fire when the primer is struck, and you feel that's a problem with the primers in that lot of ammo ... then the "Captain Obvious" in me says "Don't use those primers anymore.

Right. If you are under the impression I loaded them, I am sorry, I didn't. They were purchased from PSA. I am trying to find out if there is any adjustments or safe alterations that can be made to make the ammo function as intended.

 

[Marvet85]

I’ll buy your Geissele

No idea what it is worth and why people really want it. I thought it was cool when I got it but I think it is way out of my league haha.

 

[fdkay]

The way I'm reading it, only the AAC ammo is a problem.
That kinda narrows it down.
Will your fired brass chamber? (Before resizing).
Also, get one of these.

Case Gage-CG-

 

[Marvet85]

The way I'm reading it, only the AAC ammo is a problem.
That kinda narrows it down.
Will your fired brass chamber? (Before resizing).
Also, get one of these.

Case Gage-CG-

I'm not doing my loading, does that matter? I see AAC as the problem, I am more wondering if allowing Zermatt to increase travel is worth it.

 

[MadDuner]

Looks like it just needs a teensy bit more hammer spring....like so close to setting it off.

I have to run a stiffer spring for my 5.45x39 ARs than I do my others - to compensate for harder primers.
None of the ”nice” drop-in triggers will work 100%of the time on my Russian ammo.

 

[Marvet85]

Looks like it just needs a teensy bit more hammer spring.

How does one achieve that? Factory?

 

[MarshallDodge]

Your chamber headspace could be on the long side, and the AAC ammo could be on the short side. This would cause the loaded round to bounce off the firing pin and not get allow a good strike.

I would try turning your barrel in to the action an 1/8th or 1/4 turn to make the headspace a little tighter.

 

[MadDuner]

How does one achieve that? Factory?

Just a single example:

Black Rifle Arms Enhanced Power Hammer Spring, Enhanced Hammer Spring, Hammer spring

 

[Marvet85]

Your chamber headspace could be on the long side, and the AAC ammo could be on the short side. This would cause the loaded round to bounce off the firing pin and not get allow a good strike.

I would try turning your barrel in to the action an 1/8th or 1/4 turn to make the headspace a little tighter.

Is the normal sound/symptom of that a soft thud?

 

[Marvet85]

Just a single example:

Black Rifle Arms Enhanced Power Hammer Spring, Enhanced Hammer Spring, Hammer spring

I think the firing pin spring may need to be adjusted, not sure I can do anything about a hammer spring in the bolt itself.

 

[Cascade Hemi]

Firing pin protrusion

 

[Marvet85]

Firing pin protrusion

So do you think I should send it in and have them increase it by 10 thousandths?

 

[MadDuner]

Is the normal sound/symptom of that a soft thud?

I don’t know about the actual sound - other than no BANG!

I think the firing pin spring may need to be adjusted, not sure I can do anything about a hammer spring in the bolt itself.

Ooff.
I didn’t catch that it wasn’t an AR.
I should not post until after my morning caffeine fix.

 

[Cascade Hemi]

So do you think I should send it in and have them increase it by 10 thousandths?

You should measure the protrusion and set it to the correct measurement if it isn't already.

 

[Marvet85]

You should measure the protrusion and set it to the correct measurement if it isn't already.

Adjusting that seems to be a little out of my league. I am fairly certain that would require machining?

 

[TheOE800]

Have you talked to Zermatt? You need to gauge that ammo, I’ll second that.

No idea what it is worth and why people really want it. I thought it was cool when I got it but I think it is way out of my league haha.

I’ll pay what you paid plus ride to be fair.

 

[Marvet85]

Have you talked to Zermatt?

I’ll pay what you paid plus ride to be fair.

I spoke with them, they said they would need to machine 10 thou off to increase protrusion. As for trigger, let me see what I got it for. I like it, but I just picked up a TT Special Pro curved that will do the same thing for me.

 

[spife7980]

I wouldn’t have the alter the action/firing pin for what is most likely an ammo issue.

How did you headspace the barrel, go gauge?
I would measure the go gauge with a comparator on your calipers and then measure the fired cases and those that don’t fire and compare. If those that don’t fire are significantly shorter in the shoulder then that’s what’s allowing the strike to be dampened as the case has too much room to freely rattle around chamber.

 

[sloporsche]

Measure firing pin protrusion ,they all look like a light strike . If it is within spec I would suspect the bolt is not locking in the round . I had an AK do that and just about everyone said hard primers , it was the bolt out of time not primers .

 

[MarshallDodge]

Measure firing pin protrusion ,they all look like a light strike . If it is within spec I would suspect the bolt is not locking in the round . I had an AK do that and just about everyone said hard primers , it was the bolt out of time not primers .

But how do you know it isn't a headspace issue?

I've had very similar issues in a 223 with a barrel nut. The nut started to loosen and the barrel unscrewed a small amount, which increased headspace. Lots of failures to fire until I figured out headspace was the issue.

 

[264win]

If it was mine, I should shorten the headspace a little and try again. Good chance that will solve the issue. You could also remove your extractor and chamber a “ dud “ round. See if it is snug in the chamber or loose.

 

[Cascade Hemi]

Adjusting that seems to be a little out of my league. I am fairly certain that would require machining?

The firing pin protrusion is adjustable. Call Zermatt, either have them instruct you how to do it or send the action to them.

 

[sloporsche]

But how do you know it isn't a headspace issue?

I've had very similar issues in a 223 with a barrel nut. The nut started to loosen and the barrel unscrewed a small amount, which increased headspace. Lots of failures to fire until I figured out headspace was the issue.

he said he checked headspace iirc

 

[MarshallDodge]

he said he checked headspace iirc

Yes, but is the headspace shorter on the AAC ammo? Could have some tolerance stacking or ammo that is short.

 

[DedicatedShooter]

I didn’t see this mentioned but have you pulled a bullet to check if there’s powder inside? Just a thought. I’ve done that before with reloads by mistake, early on in my reloading days however. Don’t ask me how lol.

 

[sloporsche]

Yes, but is the headspace shorter on the AAC ammo? Could have some tolerance stacking or ammo that is short.

i am only giving " checking 101" advise to check the basics then i suspect he needs to go back over his work and look for an OOF owner occurred fault

 

[sgtsmmiii]

But how do you know it isn't a headspace issue?

I've had very similar issues in a 223 with a barrel nut. The nut started to loosen and the barrel unscrewed a small amount, which increased headspace. Lots of failures to fire until I figured out headspace was the issue.

If it was mine, I should shorten the headspace a little and try again. Good chance that will solve the issue. You could also remove your extractor and chamber a “ dud “ round. See if it is snug in the chamber or loose.

My thoughts, too. To me, this is the easy (first) fix.

 

[fdkay]

I'm not doing my loading, does that matter? I see AAC as the problem, I am more wondering if allowing Zermatt to increase travel is worth it.

You can use it to check the AAC ammo.
If the ammo gages correctly, it might be a hard primer issue or a tolerance stacking issue.
I wouldn't modify my firearm because one brand of ammo doesn't work.
AAC ammo doesn't have the best reputation.

 

[Cascade Hemi]

The TL3 is a CRF action, it's not headspace.