Accuracy International AXMC .338LM - Firing Pin Stuck?

[Monk Medic]

4 month old and About 420 rounds down the pipe, my rifle went down in class today.
Shot two rounds, then “click”, firing pin moved forward only a few millimeters, still protruding from bolt housing back.
Checked primer, no contact with firing pin.
Checked safety, wasn’t on, recocked bolt, moved safety, no problem.
Removed the bolt, inspected it, reinstalled, one more round then click.
Same symptoms.
Took gun out of service.

Some notes:
This happened one time before, ironically at the same firing line, 1,000 yards, but corrected after I cycled the bolt.
The safety has always felt “notchy”, not smooth to put on or off, but being a bolt gun not a big deal.

I’m mechanically inclined, armorer for most SIG products (but no AI).
Any thoughts of where to start?

I could remove the bolt and send it off to Mile High, sure it’s still in warranty, but would like to resolve locally if possible.

Thanks!

 

[W54/XM-388]

Disassemble the bolt, pull out the firing pin assembly, clean and flush the bolt housing out & then re-assemble.
Most likely a piece of primer flew in the hole & jammed it, or some other piece of debris did.
Happened to me the first couple shots with my AWSM and then never again.

 

[Supersubes]

Like W54 said, pull the striker assembly out and inspect closely.


I don’t think mile high would bat an eyelash at fixing it after any duration, warranty period be damned.

 

[Monk Medic]

Achivement Unlocked.
Thanks @Tack425 and others for all the feedback and tips!
Also @W54/XM-388 nailed it, see below.
I’ll share this in case it might help someone else.

Was able to disassemble the bolt and insect for failure mechanism.
Found 3 primer chips/debris stuck in the bolt housing, preventing the firing pin from going forward. Always have shot factory Lapua Scenar ammo, so surprised to see this.
Appears that some of the primer case must break off, stick to the firing pin and then get pulled back into the bolt body.

Rather clever design, allows one to field strip and service the bolt very easily with no tools. I also took apart the firing pin safety block, cleaned and lubricated that. It’s been “notchy” and hard to move, a little Milcom TW25 did the trick, like glass now.

I’m going to monitor this, since the failure occurred right around 400 rounds, think a good service protocol would be disassembly of the bolt every 200-250 rounds or so to check for debris.

Cheers.

 

[Tack425]

Glad you got it working!

 

[Supersubes]

Probably be wise to figure out why it’s doing that. Perhaps look back at your brass if you’ve been shooting factory. Maybe it was a hot lot of ammo. If it’s your handloads, back then down. When a primer pierces, the resulting torch coming out of the hole tends to erode the end of the pin and the bolt face, which leads to more piercing.

 

[MACHTECH]

Treat that bolt assembly to a day at the spa at LRI?. Let Chad bush the bolt housing and turn the firing pin down to the small f/p diameter. That won't happen anymore!

 

[Monk Medic]

@Supersubes - I did check the firing pin, thanks for the suggestion, does show no wear or deformity. I’m not an AI armorer, rather a SIG armorer, so I hesitated to adjust the length, if it was even indicated.

@MACHTECH - Thanks for the tip my friend, can you elaborate a bit on that? I’m not familiar with that process and the benefits. Thanks!

 

[MACHTECH]

I had the same problem with mine. It's called primer flow. The problem is that on the AXMC with the hotter magnum calibers, the firing pin clearance hole is too big and let's small shards of primer thru the opening. After a few pieces get in there, they start jamming things up. LRI has a service where they will turn your firing pin head diameter down to the small firing pin dia. and install a bushing in the bolt face where the pin comes thru. The tolerance of the new clearance hole is way tighter than factory. This process eliminates primer flow. It is not that expensive and turn around time is two weeks or sooner.

 

[Monk Medic]

I had the same problem with mine. It's called primer flow. The problem is that on the AXMC with the hotter magnum calibers, the firing pin clearance hole is too big and let's small shards of primer thru the opening. After a few pieces get in there, they start jamming things up. LRI has a service where they will turn your firing pin head diameter down to the small firing pin dia. and install a bushing in the bolt face where the pin comes thru. The tolerance of the new clearance hole is way tighter than factory. This process eliminates primer flow. It is not that expensive and turn around time is two weeks or sooner.

Thanks for the tip my friend, can you elaborate a bit on that?
I’m not familiar with that process and the benefits.
Is that something endorsed by AI, or just general knowledge?
Thanks!

 

[MACHTECH]

I would call the guys at Mile High tomorrow. If you send your bolt assy. to them for this problem, they will send it to LRI as well. I don't think you'll get AI to admit that there's a problem if that's what you're asking.

 

[MACHTECH]

Here's what it will look like when they're done:

 

[Monk Medic]

I would call the guys at Mile High tomorrow. If you send your bolt assy. to them for this problem, they will send it to LRI as well. I don't think you'll get AI to admit that there's a problem if that's what you're asking.

Thanks, do you have the name of the service contact at Mile High?

I did go on LRI’s website to review the process, they have a nice explanation, well documented. I was concerned about the note it will change head space, did you notice a difference?

I’ll call both places tomorrow to understand more about your suggestion. Thanks for taking the time to reply and explain things in detail.

 

[Supersubes]

Here's what it will look like when they're done:
View attachment 6909672

To my lightly calibrated eyeball, that protrusion looks huge!

 

[MACHTECH]

To my lightly calibrated eyeball, that protrusion looks huge!

Thank you! It's not too often that someone tells me my protrusion looks HUGE!

Kidding aside, I thought so too. It has run flawless since the conversion though. I have since sold the rifle to another hide member and he's not had any issues.

 

[Monk Medic]

Range Report: Ran 50 rounds through the rifle after the bolt cleaning and service.
Thought I'd check the bolt and see what I find.
Removed and disassembled on the bench while still at the range, easy peezy now, takes less than a minute.

One primer flow "cup", at least that's what they look like, little cups, broken off the primer, and captured inside bolt body.
Rifle did not malf, but thinking that's only a matter of time.

Didn't have time to call Mile High last week due to my other job, but think that's on the top of the list this week,
at least in terms of outside activities to handle.

Thanks to all for the feedback and suggestions!

 

[morganlamprecht]

i would get this taken care of before shooting much more, or switch ammo...piercing primers can start fire cutting/deforming your pin and lead to piercing more often, and require the pin to be refinished also if it gets any burrs or sharp edges on it

 

[Robben]

Achivement Unlocked.
Thanks @Tack425 and others for all the feedback and tips!
Also @W54/XM-388 nailed it, see below.
I’ll share this in case it might help someone else.

Was able to disassemble the bolt and insect for failure mechanism.
Found 3 primer chips/debris stuck in the bolt housing, preventing the firing pin from going forward. Always have shot factory Lapua Scenar ammo, so surprised to see this.
Appears that some of the primer case must break off, stick to the firing pin and then get pulled back into the bolt body.

Rather clever design, allows one to field strip and service the bolt very easily with no tools. I also took apart the firing pin safety block, cleaned and lubricated that. It’s been “notchy” and hard to move, a little Milcom TW25 did the trick, like glass now.

I’m going to monitor this, since the failure occurred right around 400 rounds, think a good service protocol would be disassembly of the bolt every 200-250 rounds or so to check for debris.

Cheers.


View attachment 6909409

how many in-lbs did you torque the two attachment screws?