300 Blackout kaboom: squib or double charge?

If you had a barrel obstruction causing a kaboom, I think you'd have a bulge in the barrel where the front of the second met the back of the first.

Also recall that if the preceding bullet squibbed, it would have had to make it past the gas port in order to function the action.

Based on memory, I think a double charge of H110 will fit in the case, so that's possible.

ETA: I confirm 9.5gr H110 is reasonable data, and 20gr would not prevent the bullet from seating (although it might be compressed).

How did you determine the load data?? 9.5 grains of H110 seems hot to me, especially with the 220gr spire point, but I don’t have ready access to my reloading data.

It sounds like a case head separation to me. Do you know how many times that brass had been loaded or trimmed?

Sounds more like a gun issue than an ammo issue to me. Been a while since I loaded 300BO but I didnt think a double charge would fit in case with a deeply seated bullet. I have been wrong before

Have you tried a shorter OAL yet? If you could live with seating that bullet a bit deeper - 2.11ish, you will more than likely catch a double charge next time around. Gotta be gobs of empty space left over with a 9.5gr charge under that bullet seated @ 2.20

GONRA sez yer DAM lucky it wasn't WAY WORSE!
That's the worst Kaboom (cracked receiver)! WOW!)
I've seen on these websites (under .50 BMG caliber).

Slow down and review everything yer doin' .....
START OVER.....

Or else its gonna HAPPEN AGAIN!

BRASS- A loaded rounds outside neck diameter should not be larger then .334" If larger, bullet may get crimped in the chamber when loading. Pressure would be high. Some necks need reamed out.

Plated bullets? Hodgdon data uses 220 GR. SIE HPBT. If bullet moved out of the case on being chamber, may cause a problem.

Double charge, could be?

Not a barrel obstruction IMHO.

Did you use a magnum primer? Data calls for a magnum primer and though most powders dont need it H110/W296 need that extra ignition. Not saying its the problem at all just passing along some awareness.

Visual inspection of you charge is paramount! Even with random or scheduled checking of charge weight you still need to observe the charge. Im sure i dont need to tell you this now but for those that are watching the thread and learning.

H110 doesn't do well with under charges either. Not saying evidence indicates this but its a well documented thing with H110/W296. You do not want an undercharge with these powders.

Some people may disagree but IMHO H110 is one of the worst powders to use for 300 Blackout.

I would say double charge though using Quickloads that would be a very compressed load (~117% of useable case capacity with bullet seated to 2.260) to get 19gr of H110 in a case under that bullet. I have the Berry bullet already entered into Quickloads as that is my favorite subsonic plinking bullet.

If it had been a normal charge even if the case failed there would not be enough pressure released into the barrel extension to do the damage the OP reported. At normal pressures a case failure would have blown out the magazine but not damage the bolt and upper. That takes serious pressure to achieve that damage even in the case of a case head separation. Quickloads is saying 9.5 gr under a 220gr Berry bullet is only generating 17 ksi but a 2x charge take that well over 100,000 ksi.

I’ve had case head blowouts in my .308 M1a… it blew the guts out of the magazine but otherwise didn’t do anything. This really sounds like… if not a double charge, then some mix-master-mishap of charge weight/bullet/case.

Wow ... thank gosh no one was hurt.

I've used a bunch of H110 in my 8" 300 BLK and you can definitely double-charge if not careful, which is what it reads-like to me.

Wish you had some pictures to share - they're always helpful.

Really doesn't read as if it was a squib-caused obstruction. The description of the damage definitely would imply that the catastrophic failure occured in the chamber. Either a double charge or a case head separation but I've had case head separations before that were ugly but not the kinda ugly you are describing.

It had to be a squib because there is not enough room in the case to get a double charge.

I'm going to walk back out to the man cave and check case capacity with H110 in 300 black ... I'm using N120 tomorrow to roll 500 rounds but since I am already set up to go I might as well go check with some H110 .... brb.

::::::: long pause ::::::

Okay so I took four pics ....

- Full case and then the grn weight dumped

- Below the rim and then the grn weight dumped

Friend, you can definitely double charge a 300 BLK case with H110 imho.

mcb said:

I would say double charge though using Quickloads that would be a very compressed load (~117% of useable case capacity with bullet seated to 2.260) to get 19gr of H110 in a case under that bullet. I have the Berry bullet already entered into Quickloads as that is my favorite subsonic plinking bullet.

If it had been a normal charge even if the case failed there would not be enough pressure released into the barrel extension to do the damage the OP reported. At normal pressures a case failure would have blown out the magazine but not damage the bolt and upper. That takes serious pressure to achieve that damage even in the case of a case head separation. Quickloads is saying 9.5 gr under a 220gr Berry bullet is only generating 17 ksi but a 2x charge take that well over 100,000 ksi.

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I agree. Wish I had seen your post before I walked all the way out to the man cave at almost midnight just to measure and take pictures, (see above) ... but at 18.1 grains (I was going by sight below the rim without the benefit of the flash seen in the pictures) that is almost a double charge and I have no doubt another grain would go in there and that double charge could be missed if not careful .... especially in bad light or with distractions.

I never thought about running it through guickloads ... but I am glad I went and actually tried it just to see for sure.

And listen y'all, it doesn't have to be a double charge .... could have been 15 grns or 16 grns, one bad or one bad and a half powder drop, a double tap on the drop arm ... either way it really seems like an overcharged round or even maybe, I dunno, ... I dunno. There are other things it could have been but more nefarious.

Anyways ... the damage described is not indicative of a squib obstruction.

I guess we should ask for the barrel length ... I am assuming 16" but I suppose 8" might make a difference in terms of it possibly being a squibb obstruction given the previous round did not lock-back ... that's the really weird part about this.

Sorry to hear about the Kaboom but glad to know you’re ok. Double charges, while possible, are usually caught by eye if you’re watching. Any chance this could be an OOB problem? I don’t know your firearm, but perhaps a firing pin hang up or slam fire?

I guess it could happen, but I've never seen a squib by itself cause any damage unless the bullet stayed in the barrel. I've also never seen a squib that had another round fired behind it and didn't bulge the barrel.

I've experienced case failures of various kinds from splits in the web or base to classic separation. None caused anywhere near the sort of damage you have. The primary effect was a bunch of gas where it didn't belong, with some minor flame pitting around the bolt face.

My first guess would be a double charge.

My second guess would be a powder mix-up. Do you have any other spherical powders of faster burn speed in inventory? If so, is a mix up possible? I once wasted a perfectly good 1/2 can of H110 by pouring HP38 from my measure into the wrong can. DARN glad I caught that one. Ruger Blackhawks are tough, but I don't feel like touching off that blue pill!

Third guess, and a rare and controversial one at that, would be the mythical flashover detonation, which I believe you are referring to as a squib. Your loads seem in order, but....I have experienced this phenomenon with a ball powder in a much larger 30-06 case using published and trustworthy data. The result was a bent op-rod and blown primer. The catalyst I believe was a combination of relatively low load density (check in your case), extreme cold at or below zero (not check in your case), and a relatively mild primer (also not check). Powder position in the case may also have been a factor as the M1 is a "slam it home" action, as is your BO. The event was accompanied by a noticeable hang-fire, which you do not indicate in your case.

ETA: I did have an occurrence of a HEAVY charge of shotgun powder once. A piece of foreign matter had made it's way into the shot or powder hopper. I think it was a piece of the foam/paper sealant from the can lids. It jammed in the drop tube, below the measuring vessel, and some loads were very light, then it would let go a whopper at random. If you're using thrown charges and not scaling every one, this could be a distant possibility and would align with the light charge first followed by the rifle destroyer.

Dewey 68 said:

When I finished my first mag, I noticed that the bolt didn't hold open, but it didn't sound any different.

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How many rounds were in the magazine when you started and how many holes were in the target when you finished it?

Maybe some different powder left in the dispenser that was not cleared out?

Dewey 68 said:

How light does a load of H110 have to be to have a pressure issue?

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A light load that is below published data is more likely to produce a squib round. The powder will not burn correctly, because of low pressure. A crimp should be use.

SAAMI-
SQUIB LOAD
A cartridge or shell which produces projectile velocity and sound substantially lower than normal. May result in projectile and/or wads remaining in the bore.

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Dewey 68 said:

As far as how many rounds were through the paper, I didn't think to look.

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Playing with new loads, especially subsonic ones, you always want to make sure they exit.