kaboom

[ds762]

http://www.ar15.com/forums/t_3_66/548018_kaboom_.html


It's easier to link to that thread than to re upload all the pics.

:frown:

The barrel is going back to spook to be evaluated and provided it gets a clean bill of health I'll be ordering a new upper and BCG to rebuild it.

[Mister Moon]

Damn ! :mad:

[SwampF0X]

Dang man. Sorry for your loss. Do you know what caused it?

swampf0x

[Spook]

ds, Yikes :eek: Glad your not bleeding!
Q's..How many rounds of 125's did you shoot before switching over. Did they all eject OK? Was it the 1st subsonic round after?
Did the barrel come out of the upper " easily " ?
Where did the load data come from?

[rv10flyer]

Wow :eek:, glad you are OK.

[ds762]

The barrel took a couple taps to come out of the upper. Cracked extension! :frown:

http://i516.photobucket.com/albums/u324/ds762/IMAG0344.jpg

[Dacapster]

Glad you still have your digits.......that really sucks!

[BWE Firearms]

Glad you are OK.

[snipecatcher]

Somebody mentioned on the other site that you didn't have a filler to take up case capacity. I'm not sure he understands the concept that the bullet IS the filler with this cartridge. I don't think you can get enough in there for an overcharge that dramatic, a stuck bullet makes more sense to me.

[rsilvers]

A normal subsonic charge is going to be under 40,000 psi.

The concept of detonation is only for very slow powers in a large case - I doubt that happened with H110.

[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.

http://www.m-guns.com/largefoto/picts/ulfls/15092011/15936062751.jpg

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.....:eek:

[Spook]

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

[Ned christiansen]

Yes, too low for that. Woulda been one hell of a crimp too, and I'm not crimping these at all.

[Spook]

I'd like to take this opportunity to remind the board that ds762 is a trained professional... and the rest of you should not attempt this at home :mad:

[LouBoyd]

I'd like to take this opportunity to remind the board that ds762 is a trained professional... and the rest of you should not attempt this at home :mad:

I don't understand. What should we not attempt at home? Blowing up our 300 WTF rifles?

[ds762]

I pulled the remaining loads from that string of ammo and it revealed inconsistencies of charge weights and is leaning towards overcharges.
I'll be getting ahold of RCBS and see about sending in the scale for re-calibration.

I shipped the barrel to spook and hopefully next week we can determine the extent of the damage to the barrel and see if its worth saving.


In the mean time this is an excellent opportunity to remind everyone that F-ups do happen to everyone. Be safe.

[Alleycat]

I’ve had a RCBS digital scale for years. One day I discovered that it was off by about 2 grains. The problem with fliers @ the 800 yard line suddenly had an explanation. I sent it back to RCBS. $100 and five months later, I had the scale back. I was not amused.

[LouBoyd]

I would not buy dies from a balance manufacturer or a balance from a die manufacturer.
Sartorious and Ohaus are to balances what Redding and RCBS are to dies.
http://precision-toploading.balances.com/

I use a 20 year old Sartorius and it's still within 2 milligrams. Part of using any balance is routinely checking it with a calibrated weight. Blowing up one firearm is more expensive than a good balance.

Handloading is dangerous but so is driving. One mistake in many things we do could be lethal.

[Alleycat]

RCBS scales are made by Pact. Pact also makes scales for several others. I use two scales that check one another. Anything can fail regardless of cost or quality.

[mstarling]

My training is as an analytical chemist. Is good to check a reference weight at the beginning of a loading session regardless of the kind of weighing device you use. The few seconds it takes can avoid the one event you'll never forget (if you're lucky).

[martineta]

RCBS scales are made by Pact. Pact also makes scales for several others. I use two scales that check one another. Anything can fail regardless of cost or quality.

I am sufficiently scared to put my back-up balance beam scale back on the bench to double check what my electronic scale is telling me. That and of course eyeballing every powder drop in the case to see that they look the same. Never had anything like that happen but a first could be a last.

Thanks for pointing two scales out.

[LouBoyd]

I am sufficiently scared to put my back-up balance beam scale back on the bench to double check what my electronic scale is telling me. That and of course eyeballing every powder drop in the case to see that they look the same. Never had anything like that happen but a first could be a last.

Thanks for pointing two scales out.

A set of calibrated weights is cheaper than an extra balance. I'm not against having a second balance as a spare, but if the two don't agree you still need a reference weight to tell which (if either) is correct.

There are a lot of ways to mess up with any balance. The most likely one is to improperly tare the tray used to hold the powder being measured. The balance itself doesn't have to be defective to give wrong readings.

Make sure your body, bench, and balance don't have an electrostatic charge both for weighing accuracy and safe powder handling. There are pros and cons for using conductive and non conductive tools. There is slightly more spark hazard with metal tools but they greatly reduce electrostatic errors. I use a metal bench and metal chair on a bare concrete floor. Basically the same setup as for handling semiconductors.

How many of you weigh each of your loaded cartridges? I reject any cartridge which is more than 1% from the average. With heavy bullets and small charges of fast powers (45 ACP for example) that will always detect no powder or double charges though it doesn't insure velocity consistency.

[HUNTER2]

FYI, I shoot a lot of 180 Speer btsp backwards for a plinking load in bolt and single shots. Make a very nice hole and yes they will kill deer. Tried to use some Nosler bt's ( base the bt was larger ) and they are recovered wasp waisted like your example. Also acc stinks. reason >?????