LooseRounds.com5.56 Timeline


Parts Gun Kaboom

A B-ARFCOM user reported this Kaboom today and there is much discussion on the cause.

I pull the trigger and Kabloooey!!! Shit flying, smoke all over and both thumbs are numb on the pad.  

I look down, magazine spring hanging out, follower pieces on the table.  I checked myself to see if I was bleeding or missing parts. Nope, but my gun was messed up. The door was bent out and I couldn’t get the bolt to go in or out.  Shit, time to go home.  I checked my target, and there were 7 holes, just like there should be, so no problem caused by a bullet stuck in the bore.

All pissed off all the way home. Once there I got the  bolt/carrier to go back easily by poking it out from the muzzle with a metal rod.  The body of the case was still in the chamber.  Then took the buffer/stock off and bolt/carrier came right out. Absolutely NO damage to the Aero lower.  

The bolt itself has a missing lug and the extractor is bent and chipped. The bottom of the carrier that picks up the new cartridge from the top of the mag is completely blown off like somebody cut it with a knife. You can see the bolt in the channel. Holy shit never seen nothing like it.  

The door is wiped out and the bottom of the upper is kind of blown out. I thought possible a broken case in the chamber affected the pressure and blew up my gun.  I was looking for a tool to use to pull out the casing.  As I flipped it over the case fell right out on the floor. The head has a section missing but the front is just fine and in good shape.  I cleaned out the chamber and bore and everything looks just fine.

I honestly thought it was a bore obstruction, but now it looks like I might have a discharge when the bolt was not in battery, like not all the way forward.

That shit really shook me up. My thumbs were numb for an hour, and it took me a few minutes to realize what just happened.  If it fired out of battery, how the hell did that happen. All I can think is that the carrier got damaged during the previous (6th)shot. And when I touched off the 7th shot the damaged carrier parts came apart and let it hit the primer before it was in battery.

First time for everything.

7 thoughts on “Parts Gun Kaboom”

  1. I note that there is limited information provided about the ammo.

    Nine times out of ten, the ammo is the reason things like this happen–Cheaply made crap with out-of-spec components. I’ve seen primer detonations take place out of battery from all sorts of weird crap, and I’ve seen even correctly-sized propellant charges do really weird shit after being taken out of storage.

    One of the things that has to be remembered is that some powders are horribly prone to going weird after high-temperature exposure. Buddy of mine down in California went on deployment for a couple of years, came home, took his stuff out of storage at his parents and went out to the range one day. Two rounds in, click—-KA-BOOOOOM. He blew up a really nice rifle, and the only thing that anyone ever figured out for “Why?” was that the propellant he’d used in the handload had gone off due to the high heat where it was stored in his dad’s garage. The primers initiated just fine, but some of the powder would do really strange things due to it having broken down. He did some sampling with a test fixture, and that stuff was all over the map–High pressure, low pressure, hangfires, you name it. Yet, when he broke it all down to check his reload work, everything was match-ammo consistent. The only common feature was the powder, which he later learned was notorious for responding poorly to high-temperature storage.

    That doesn’t look like a “parts” problem, to me… I think it’s ammo.

    • You’re right – usually these ka-booms are ammo issues.

      The powder-in-high-temps is a real issue, especially on canister powders (ie, bulk powders used for military contracts).

      Let’s back up a sec and talk about the wonderful product that is ‘smokeless powder.’ Smokeless powders come in three variants:

      – Single base – which is composed of only nitrocellulose. This burns ‘cooler’ and isn’t as temperature sensitive as the next two variants and generally work at lower chamber pressures.

      – Dual or Double base – composed of nitrocellulose and nitroglycerine or nitrodiglycol, to dissolve the nitrocellulose. They are quicker burning powders, produce higher pressures. Many modern commercial powders are double base powders.

      – Triple base – composed of nitrocellulose, nitroglycerine/nitodiglycol and nitroguanidine, a compound that suppressed the muzzle flash. This last issue makes military contracts the primary consumer of triple-base powders.

      OK, so when we start talking of decomposition of smokeless powder, you see that there can be some high-energy components to come out of composition here. One of the ways you can tell that your powder is decomposing is to open a container or cartridge, and look for a reddish-brown vapor to come off the powder. It will smell acidic. This is a sign that the powder is decomposing. Do not inhale the vapor.

      Powders that decompose under heat can have significantly accelerated burn rates. How much, I can’t say.

      • I don’t think anyone can, TBH.

        QASAS guy I used to know told me that he had been taught in training that there were some compounds they had tested which transitioned from nice, normal deflagration into really unpredictable outright detonation after storage in unmonitored high heat conditions.

        Folks who have bought any of the surplused ammo off the Israelis that was issued out to troops and then taken back will have probably experienced this. There are reasons we now blow all that crap up, instead of trying to re-issue it.

  2. Sounds like what happened to me..Had a eagle arms build from 1999 and was shooting some tzz headstamp that i picked up on the cheap at a springfield mo gunshow.
    Ripped the bottom off the case and blew the thermold magazine apart.
    No one was hurt but the magwell was swelled up..live and learn i guess


Leave a Comment