kaboom

[Rancid Coolaid]

8 grains of H110 doesn't take up much case capacity, he could have added multiple charges to the same case.

However, I hate H110 and won't use it again on a 300.

[LouBoyd]

What was the load >supposed< to be? Where did the cartridge come from? On the ar15.com site a load of 8 grains of H110 with a 208 grain AMAX was mentioned on the tread about this blowup but it wasn't clear if that's correct. That's a 1000 fps subsonic load but I can't say if it's suitable for that particular AR-15. Low case fills rarely give good accuracy.

A double charge (16 grains of H110) would fit in the case (96% fill) and would produce about 70kpsi per Quickload and seems the most likely to shear the locking lugs though the bolt damage seems like more pressure.

A second bullet lodged just started in the bore would be under 30kpsi and if a second bullet were further down the bore the damage would be different. Iif a bullet were lodged in the throat it might push the bullet in the cartridge into the case. Too many variables there to calculate properly but I don't think even that would exceed safe pressures.

A 100% case fill of Bullseye or N310 would produce about 105kpsi. That seems to me consistent with the bolt damage but I don't see how that could happen by accident.

Just speculating. There are many possibilities.

[Titleiiredneck]

Secondary explosion, double charge, and thats a 800ish fps load so a stuck bullet could cause this so there are a few possibilities there. My vote is for a secondary exosion with the low case volume and/or a stuck bullet.

[Alleycat]

Do you have any rounds left over?
Have you weighed the loaded rounds?
Do you weigh all subs before you shoot them?
Did you have A-Max and V-Max bullets on the bench at the same time?
I use H110 for supers and VV N110 for subs. H110 works great in supers and can work well in subs, but it is a heartless soulless bitch if you goof up a sub. I weigh each and every loaded subsonic round. I hate that this happened to you. Not knowing what happened is the worst. I’m not trying to second guess your reloading. I’ve been reloading for 20 years and I have made mistakes. I have been lucky enough to catch them. I started using a clear funnel several years back and witnessed my first bridging soon after. I always wondered how many times it had happened before and I never knew. You could have done everything perfect and bridged one round.

[Ned christiansen]

I have a couple random, unqualified thoughts here.

LouBoyd, just to put your 70,000 PSI figure in context, a friend of mine did some pressure testing to quantify the effects of shooting 5.56 NATO ammo in a .223 SAAMI chamber, and he regularly got 72K and even got above 76K! This happens thousands of times a day all across the country.... which is not to say that the occasional "unexplained" KaBoom doesn't take place because of it.

I know this thread is not about .223 but I thought this might build some context around your numbers.

But check this out: me, shooting 240 SMK handloads. I recover one from gel and observe an odd "waist band" on it. I look and think, think and look, and measure it. The bullet diameter is reduced to .299 in this area, and this area occurs just below where the neck of the case would be holding the bullet.

When loading this batch, I had decided, no more 240 SMK's, they are just too dang long. It was too much finessing to get the bullets seated deep enough-- what with powder being in the way (I considered for a moment, what if I just started them all, then turned the press upside down, so the powder would not be blocking the seating of the bullet?).

So there I am with some 240 SMK loads, the base of the bullet practically capping off the flash hole. There is little to no powder under it, it's all to the side.

My Bubba-tastic conclusion here: As pressure built in the case, there was plenty of bullet shank for it to act upon, and very little base. Before bullet movement started, giving the pressure an avenue of relief, the pressure actually pressed on the bullet shank, collapsing it. This (to me) explains why this only happened from the bottom of the case neck down.

Now-- if this could happen this much, could it not happen some more? An event whose timing is just a little different, say the bullet delays even more in getting moving, the waist of the bullet caves more, and the displaced metal moved down, increasing bullet diameter, adding to the problem?

I'll find the pics of this bullet and get 'em up.

[Ned christiansen]

Here 'tis. You can see where the waist was so reduced that the rifling did not have anything to engage.



Revisiting this just now, with a sectioned case, the bullet was of course not actually down on top of the flash hole, but that was a perception when loading them-- as the bullet seated on top of the powder. Seating depth pretty much coincided with case volume coming to zero. I was specifically trying to get 240's to load a little on the shorter side, emulating more or less the Remington 220 sub load's COAL.

[mstarling]

We know that some powders such as H110/WW296 are more prone to detonation than are others.

Anyone know if Hercules 2400 is prone to the that problem?

[fasttwist]

Was accuracy or stability affected by this? Can you reproduce it to prove your theory? I have seen pictures before and this was discribed as bullet elongation or deformity due to tumbling. No rifiling = unlikely.

[Ned christiansen]

I agree Paul, with no rifling in the waist, safe to say it left the case this way. I don't believe it tumbled anyway as it went through 20-plus inches of gel and stopped on an armor panel.

One opinion was that it was made this way-- I don't believe it. I'd have seen it upon loading, or felt it with my fingertips, or felt an odd variance in effort as I seated it. The top of the waist corresponds perfectly with the bottom of the case neck.

Anyway, knowing how these are made, would you not agree that it's very unlikely to have been made this way?

And.... as to recreating this..... I don't think I want to.....

[Spook]

looks like the effect of a crimp but they're seated a little farther down for that to the the case