My AK blew up

[Funderb]

I understand the concept of slamfire well, but the way you put it, the pin just slid into the primer on the round he made, like it was still floated.
If that were the case every single chambering would be a slam fire.
If you look at the pictures you will see the primer has been smashed pretty well by the firing pin. I just cant fit slamfire into the picture, but hey I wasn't there.

 

[Slamfire]

You know jacketed bullets are meant for use in self loading weapons for a reason right?
Because regardless of the precision of the firearm or not, chances are that the actual bullet is going to scrape a little on the edge of the chamber.
More than likely the cause of the weird out of battery accident is lead buildup around the rim of the chamber.

I agree with you about using only jacketed bullets for semi automatic weapons. The use of lead bullets does increase the risks of creating a lead ring, or leaving lead particles in the chamber.

I had not thought of this when I wrote my reply, I think your explanation is also plausible.

A free floating firing taps the heck out of a primer. It reaches its highest energy point just as the bolt lugs engage. At that point the bolt has reached its highest velocity but stops. Since the firing pin is still moving inside the bolt, it will tap the primer at a decent speed.

We have all seen the primer indentations on unfired rounds.

In either case, the bolt had some lug engagement or things would have been much worse.

 

[TargetTerror]

I talked to a local gunsmith, and I'm going to have him check it out and make sure everything is ok.

There are a couple of facts that I may have implied but not stated outright that should affect some of the analyses I'm seeing. First, this was literally the 6th or 7th handload that I fired out of this gun, ever. Everything else had been Wolf FMJ. As such, I seriously doubt leading of any part of the chamber or barrel was to blame. I buy the arguments that lead will shave off somewhat in the chamber and off the gasport, but that should only happen after many many rounds. I've read too many reports of people shooting lead in AKs and SKSs without problems to believe that 6 rounds would cause such a catastrophic failure. I don't know the exact hardness of these bullets, but since they had gaschecks, they were clearly designed for higher velocities.

I also don't buy the slamfire argument, because the gun did not slamfire. I chambered the round, slowly took aim, and then pulled the trigger. The round went off when I pulled the trigger, not when the bolt closed. There was probably at least 5-8 seconds in between closing the bolt and pulling the trigger. A slam fire should occur immediately, correct?

I also check and yes, I could fit a double charge of 2400 in the case. But, that would have been a VERY compressed load, which I'd hope I'd have felt. The powder was may 1/3 or so of an inch away from the top with the double charge. Also, the bang when this round fired didn't see all that excessive - it just seemed like it came from the rear of the barrel instead of the front. I don't have any other experiences with such failures, but I'd think a severely overpressured round would sound VERY loud.

Thanks, and keep the opinions coming, I'm curious!

 

[kcmarine]

I'm still kind of amazed that's all it did to the gun. Sheesh those things are durable.

 

[SSN Vet]

O.K.

slamfire is off the table....

so, for some reason the bolt did not rotate and engage the lugs.

I still want to know wheter you re-sized the new brass.....

and again...that bullet was designed for a tube fed lever gun.....

so either the head space was off because the brass was not sized

or ....

the FN bullet was seated to far out and even though the OAL was in spec. the fat ogive just behind the FN engaged the rifling and prevented the bullet from chambering all the way.

I can go either way....but please tell us whether you sized the brass, and if you didn't, size a couple and compare to the un-sized new ones and see how the shoulders compare.

as for shooting cast bullets in AKs and SKSs....

http://castboolits.gunloads.com/showthread.php?t=13453

If Ed Harris says it's O.K., that's good enough for me.

if it ever stops snowing, I'm gonna smelt my first batch of wheel weights and get casting....I've got the .312-155 Lee mold gathering dust on my bench.

 

[JesseL]

If the gun hadn't been completely in battery, I doubt it would have been so difficult to open the bolt.

I still think the shoulder was pushed too far back and the round was further into the chamber than it should have been.

 

[TargetTerror]

I still want to know wheter you re-sized the new brass.....

and again...that bullet was designed for a tube fed lever gun.....

so either the head space was off because the brass was not sized

or ....

I full length resized the brass, but did not trim it. Actually, I full length sized minus maybe 1/8 inch - with the die touching the shellholder, there was a TON of force required to finish the downstroke and begin the upstroke. Yes, I lubed the cases and the inside of the neck.

 

[JesseL]

What brand of dies are you using?
How much did the length of you other fired cases change?

 

[Funderb]

I had two wrecks in 1.5 minutes on my bike tonight,
I feel like your AK.

But to answer the second part of the OP,
yeah, the bolt is probably screwed.
But the gun most likely is completely salvageable.

Slamfire:
I hear you on that one. I am used to the sks pin though, it's a pretty light one. The AK pin is much heavier right? It could keep more forward momentum even just slightly out of battery.

 

[Slamfire]

I also don't buy the slamfire argument, because the gun did not slamfire. I chambered the round, slowly took aim, and then pulled the trigger. The round went off when I pulled the trigger, not when the bolt closed. There was probably at least 5-8 seconds in between closing the bolt and pulling the trigger. A slam fire should occur immediately, correct?

Agreed. This was not a slamfire.

I hear you on that one. I am used to the sks pin though, it's a pretty light one. The AK pin is much heavier right? It could keep more forward momentum even just slightly out of battery

I have not weighed either, but there have been enough slamfires with Chinese SKS rifles that lawyers were trolling for clients within the pages of Shotgun News. They had adverts.

And it was all due to firing floating firing pins and sensitive primers.

 

[alsaqr]

Look at the upper left photo of the case head. Look at the upper portion of the photo. It looks like there was very little good metal in that area. It looks like a classic case head separation. How many times was that case re-loaded?

 

[Funderb]

well, I sure am glad I can't afford to buy anything other than milsurp and wolf!

oh by the way, I like your signature line,
I always argued that accuracy lay with the shooter,
and precision with the firearm.
kudos.

 

[dmftoy1]

If you can fit two charges of 2400 in there and are loading on a 550 then my vote is for a double charge. (Purely a wild-assed guess). I think that given the leverage advantages that a compound linkage offers on a press that it'd be pretty tough to differentiate between the add'l effort to compress a load and the effort you're expending to FL resize a case, seat the bullet, compress the powder measure springs, etc.

I'm glad you're ok! I guess it's a testimate to that rifle that whatever happened only scared the bejesus out of you and didn't hurt any one.

Have a good one,
Dave

 

[Feanaro]

dmftoy1: The primer doesn't seem to have an over-pressure signs from where I'm sitting. Notice how the rim is blown out to one side. Look to me like it fired out of battery.

 

[Hokkmike]

Great post - thanks!

 

[dmftoy1]

dmftoy1: The primer doesn't seem to have an over-pressure signs from where I'm sitting. Notice how the rim is blown out to one side. Look to me like it fired out of battery.

I agree with you that the primer doesn't show signs of overpressure, but the fact that that the ammo felt "hotter" to him and hit closer to POI would indicate to me that this round was running faster than his others. I'm definately no expert, but I wouldn't think that firing out of battery would "increase" the pressure and speed of the bullet. Of course it's all conjecture on my part. If it did fire out of battery, what causes the cover to go flying off . . is that gas escaping around the case or something? (ak ignorant here)

Regards,
Dave

 

[alsaqr]

He says that he loaded the round by hand. That rules out slam-fire and a bunch of other stuff.

That leaves a normal case head separation or a case head separation due to an overload. In that AK the rear of the cartridge case is not supported by the chamber. More than 1/8 inch of the case sticks out of the chamber when the bolt is closed. Unfortunately, this is right at the place where a case separates.

A cartridge case stretches when fired. The area impacted by this stretch is the inside junction of the case head and case body. A depresssed ring forms inside the case. Sometimes you can see a bright ring around the head of a case, usually one that has been re-loaded several times. This is an indication that a case head separation is imminent.

I do not believe that the case had a double charge of 2400. 29 grains of 2400 would have probably blown the bolt out of the gun.

It ain't a really good idea to load 2400 in a 7.62x39 case. Use a powder that will overflow the case when there is a double load.

 

[SwampWolf]

There is a difference between "slam fire" and firing-out-of-battery. A firearm slam fires when the round is chambered and the bolt goes forward into battery but fires without the trigger being pulled (usually indicative of a sear/disconnector/interrupter trigger problem). If the weapon can be fired with the bolt not seated properly, it is said to be firing "out-of-battery". Both conditions are defects but only firing-out-of-battery will cause damage to the firearm. A properly designed firearm in good condition should never fire out-of-battery, no matter the condition of the ammunition or the degree of dirtyness in the chamber.

 

[DBR]

The OP says he resized the brass but did not check for case length. If the case neck extended into the rifling lead, pinching the bullet, it could cause serious over pressure.

This has happened when 5.56 ammo was fired in .223 chambers. Tests I have seen suggest that normal pressure of about 55,000psi can go up to close to 70,000psi when this happens.

Just a guess.

 

[Slamfire]

Both conditions are defects but only firing-out-of-battery will cause damage to the firearm. A properly designed firearm in good condition should never fire out-of-battery, no matter the condition of the ammunition or the degree of dirtyness in the chamber.

I have had out of battery slamfires and within battery slamfires in Garands. Then I stopped using Federal primers.

The M16 had slamfires early in its deployment, so the services redesigned the firing pin. They made it lighter. However they also controlled the sensitivity of the primers loaded into military ammunition.

What I am getting at is the statement of "properly designed". There are a lot of military weapons out there with free floating firing pins. Slamfires are controlled by primer specifications. So why did the military not add active design measures? maybe they did not want to stock an extra part. Maybe they thought they had enough parts as is and did not want to add more parts, and more unreliability into the system. And they were not building weapons for Bubba the reloader. They were building weapons to be used by their troops with issued ammo.

So when the military surplus weapons get out there, into the hands of Bubba the reloader, Bubba is going to be surprised when his soft shell primers go boom without having to pull the trigger.

And the weapon designer?, he is going to say, "not my problem".

 

[jhallrv4]

That chamber face is normal for a Romy. (second pic) Both of mine look exactly like it. They fire fine. I've seen others, looked like it too.
Looking at the third pic, the ogive of the two bullets are quite different, your seating die is going to be confused as how far into the case to push the lead bullet!
Jeff