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View Full Version : PMC X-TAC 55gr, a bit on the spicy side.


One More Time
05-30-23, 18:51
Ran across this today, no one sprung a leak but the upper is done for.
Lot # in link with pics, some pretty spectacular carnage.
https://www.northwestfirearms.com/threads/pmc-5-56-ammo-blew-my-rifle-up.451096/
markm
05-31-23, 11:23
Ammo quality has suffered recently.
Disciple
05-31-23, 11:37
What's the mitigation? Weigh every cartridge individually to check for over-charge, or would that be paranoid?
georgeib
05-31-23, 12:07
What's the mitigation? Weight every cartridge individually to check for over-charge, or would that be paranoid?

Didn't think you could dramatically overcharge a rifle round as the case is almost full as it is.
Disciple
05-31-23, 12:39
Didn't think you could dramatically overcharge a rifle round as the case is almost full as it is.

What else would cause this? I don't see how you would have only one cartridge out of a box with the wrong powder unless deliberate sabotage.
kerplode
05-31-23, 12:50
I dunno...I'm always a little skeptical of these reports.

Last time I saw an AR blown like that it was because a dude's "friend" fired a 300BLK in a 5.56 chamber. I saw that one in person and it was pretty similar damage. The bullet was sticking out of the muzzle and was like 2.5" long. Upper was blown to shit.

To get those pressures in a 5.56, it'd have to be a completely inappropriate powder, obstructed bore, oversized projo, or somebody not telling the full story...
markm
05-31-23, 13:04
Didn't think you could dramatically overcharge a rifle round as the case is almost full as it is.

Depends on the powder. Some of the faster powders are high "ullage" where they're at max with a good bit of room left in the case.
georgeib
05-31-23, 13:24
Depends on the powder. Some of the faster powders are high "ullage" where they're at max with a good bit of room left in the case.

Ah, okay. Any idea if that's what PMC uses? An overcharge would definitely be the simple way of explaining it.
markm
05-31-23, 14:19
Ah, okay. Any idea if that's what PMC uses? An overcharge would definitely be the simple way of explaining it.

I don't know about PMC's stuff. I'd guess it's a ball powder. Depends on the burn rate of the powder and how much could be in there. We shot the overcharged AAC ammo that's actually a compressed load, it didn't blow up any guns. I'm guessing AAC's powder is a slower burn, because if it was that overcharged and fast powder, it'd have at least ruptured a case head.

But to the points made, if the damage is that bad, you would be worried about an obstruction or something.
georgeib
05-31-23, 14:27
I don't know about PMC's stuff. I'd guess it's a ball powder. Depends on the burn rate of the powder and how much could be in there. We shot the overcharged AAC ammo that's actually a compressed load, it didn't blow up any guns. I'm guessing AAC's powder is a slower burn, because if it was that overcharged and fast powder, it'd have at least ruptured a case head.

But to the points made, if the damage is that bad, you would be worried about an obstruction or something.

Yeah, that's what I figured.
Failure2Stop
06-01-23, 09:16
Looks like a case head failure due to thin/low web at first glance.
MarshallDodge
06-01-23, 09:19
I don't know about PMC's stuff. I'd guess it's a ball powder. Depends on the burn rate of the powder and how much could be in there. We shot the overcharged AAC ammo that's actually a compressed load, it didn't blow up any guns. I'm guessing AAC's powder is a slower burn, because if it was that overcharged and fast powder, it'd have at least ruptured a case head.

But to the points made, if the damage is that bad, you would be worried about an obstruction or something.
Something fast, like H322 or H4198, would have some room left in the case for an overcharge, but I'm not sure it would be able to generate enough pressure for a kaboom.

Sometimes I wonder if the manufacturer was loading pistol rounds and didn't get it all that fast burning powder cleared out of the hopper before running the rifle rounds.

PMC has a really good reputation but I've seen a lot of turnover in manufacturing since the pandemic.
Disciple
06-01-23, 18:20
Looks like a case head failure due to thin/low web at first glance.

I would not have guessed that would cause so much damage without overpressure. How does the bottom of the carrier get torn off?
AndyLate
06-02-23, 07:49
The more kaboomed ARs I see, the more I think Mr. Stoner was a genius. No harm to shooter, which seems typical for the platform.

Andy
Failure2Stop
06-02-23, 08:29
I would not have guessed that would cause so much damage without overpressure. How does the bottom of the carrier get torn off?

55kpsi (.223) is a significant amount of pressure, and the X-Tac is probably north of that given the velocity increase of it over the bronze line.
When the case head/web fails it's happening during that high pressure time.
The web separates, usually starting at the extractor slot, as that's where the head has no support, and the pressure then follows the path of least resistance.

This observation is based on experience and a few investigations that involved ammunition manufacturers' feedback.
A detailed in-person evaluation would be needed to have a high degree of certainty of either failure event, but that looks a lot like a case head failure/separation at web.
Disciple
06-02-23, 12:19
Thank you. An impressive reminder of the power that small piece of brass normally controls.
bfoosh006
06-10-23, 11:49
Ammo quality has suffered recently.

Kinda seems to run in a 5-7yr cycle... if not one manufacturer, it is another.