I have an MCX in 5.56 with recall that was implemented several years ago. Two times today while shooting, the floor plate to the magazine blew out, and smoke and powder spewed out from the breech. Magazine is the common gray, aluminum (?) magazine mfg'd in Hartford, CT. Ammo is factory Federal, 55 grain ammo, FMJ. Gun didn't jam, fail to feed, or fail to eject either. This has never occurred before, and I am probably at around 1,000 round count. So, what's going on?
Twice?? Id have been done after one! That is usually indicative of an out of battery kaboom, squib, case rupture or similar big-time kaboom when the explosion comes back and down more than it can go out the other end. While the Magwell does direct the gasses down into the mag and away from the shooter, it can mean parts breakage elsewhere.
Either your mag is just REALLY shitty and can lose its baseplate with the smallest of pressures (like... just being loaded) or there was a catastrophic failure in there somewhere.... what did the spent brass look like on each failure? No apparent damage on any of the parts? Bolt, barrel, gas system? What was the gas system set to? I know the MCX has different settings.
While you may be able to get away with bottom shelf whiskey, stay the hell away from bottom shelf tequila. - FishOn
Sounds like an out of battery ignition?
High primer / bad ammo.
Broken firing pin. (rare).
End of Earth: 2 Miles
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|Doin' what I can |
with what I got
Dude that sounds like textbook out of battery ignition. Have that rifle checked by a competent gunsmith and/or SIG.
Impressive that it apparently survived not one, but two, incidents.
Did you recover any weird looking brass? Are there any loose primers in your lower or around?
Some years ago I had problems with a combination of high Florida heat and humidity, a slightly overtight chamber, and hot AE XM193. It manifested in blown primers.
Seriously, I would not fire that ammo or that rifle again until I had contacted both manufacturers and determined what the problem was. The next failure might be catastrophic. Like, no more rifle, maybe a trip to the ER, catastrophic.
Death smiles at us all. Be sure you smile back.
Update: "magazine blow-out" problems continued with MCX with Federal American Eagle (FAE) ammo. Sent MCX to Sig and they couldn't replicate the problem. Sig sent gun back to me. I tested gun out with FAE and....had a few more stoppages...and this time, same "magazine blow-out" occurred in my Rock River AR-15! Switched to some PMC ammo in both guns and had no problems. So, I think I have a bad batch of Federal American Eagle 5.56 ammo. Interestingly, the Sig Customer Rep has seen bad rounds from every brand. I've been shooting since 2004, but I don't shoot a lot. Still, maybe it was my time... Hate to toss 300 rds.
you don't toss them. You contact the mfg. and explain what happened. They will have you send it back to them. Hopefully at this point you have brass and you ship all that too. If its bad they will replace it and most likely go looking for anymore of that batch...
“So in war, the way is to avoid what is strong, and strike at what is weak.”
What’s the lot number on your bad ammo? I have a bunch.
The ammo is the cheapest, most inherently dangerous part of the equation, so that part really shouldn't come as a big surprise. I imagine that despite that, the first thing most people do is blame the gun. On the other hand, the CS guys at the ammo company probably have had reports related to every brand of rifle.
Lot #: 2 47 R559
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