AR Ka-boom 300 BO style (not a castboolit)

[JonB_in_Glencoe]

edited: this was not my gun....or anyone I know personally, this was a fella on a facebook reloading group.

Posted today on a FB reloading group

Hi guys, I went out shooting with some friends today and had a great time... until this happened. I had a case head failure and it took out my bolt. Nobody was hurt thankfully but I'm trying to figure out what happened. I've heard it's impossible for an ar to fire without the bolt locked in but that feels like what happened. I've loaded around 700 rounds for this rifle but only the last couple hundred with this recipe.
Ar15 .300 blackout Hornady 150 sp 16.2 gr Winchester 296

after some folks asked some questions, more info came out

yeah, It's a pretty hot load. Hornady shows it at max but that's with a magnum primer. I was using cci small rifle but not magnum. I think that usually equates to about a half grain reduction.

all the brass was 556 lake city 2012 headstamp.
Anything's possible but very difficult with my setup. I use a hornady lnl ap. It uses a case activated powder measure so if it gets powder it's pretty much always right there. Once in a while a tenth off. Double charge would spill powder everywhere.

[Lead Fred]

One toke over the line

[Tackleberry41]

Guess he found out it doesn't take much when you operate that close to the edge. So its a max charge and the measure can be a 1/10 off, not a big deal. Some just have to go max charge with everything. Never seen a rule where just substituting a standard primer equaled a half grain reduction.

300BO seems to be one that people mess up alot. Know people that have them. One continued to use reloads that were blowing primers out and down into the receiver stopping the gun. He was just gonna blow em off. And continues to let the same guy keep loading for him as its just easier than doing it himself. Same guy who was supposedly sizing .311 down to fit in a 300BO, vs I dont know just buying the proper bullets.

And somebody else got 2 bullets stuck in a brand new barrel. The load data was a bit questionable. As it was trailboss mixed with something slower burning, guess there was some theory behind it. Then offered me some of his 223 subsonic reloads to try, um yea no thanks.

[Hamish]

Max charge of 296 plus possibly throwing heavy PLUS military head stamp brass,,,,,,,,,plus using sized down jacketed bullets,,,,,(possible spring back?)

Dude was certainly blessed.

[popper]

Case neck looks funny too. Possible setback & compressed load? AR slam-fire? I like that bullet in my BO. CCI SRP too. My guess he lost more than just the BCG. What FB loading site?

[JonB_in_Glencoe]

Hamish, I assume tackleberry's fella who was sizing down 311 bullets (probably CB) to fit 300BO, is a different fella than the fella I posted about.
==========

I posted the OP, cause I thought it was a chance that it was a S.E.E.. Possibly caused by wrong primer/poor ignition. But after more, continue discussion on FB, it seems more likely to be a firing out-of-battery issue, as the owner, when asked, claims all the locking lugs on the bolt look good, and the lugs inside the barrel extension 'feel' good.

[JonB_in_Glencoe]

Case neck looks funny too. Possible setback & compressed load? AR slam-fire? I like that bullet in my BO. CCI SRP too. My guess he lost more than just the BCG. What FB loading site?

PM sent

[osteodoc08]

Perhaps this is what they call.....a clue.

Some people just shouldn't reload.

i reload my 110gr Zmax with 19.9gr 296 as that is what has given me best accuracy. Some references list 20gr as max, others have listed higher. My brass looks good and there are no pressure signs I'm seeing.

[LynC2]

A too thick neck might be a possible factor also. I load for a 7.62x40 WT and have to watch for necks that are too thick with some reformed cases. That issue certainly would raise pressures off the chart.

[Preacher Jim]

Jon that fallacy that they can't fire unlocked should read highly unlikely but I had a 223 do that not to the catastrophic result you had but enough to shake my faith in absolutes case ruptured on down side gas went in the mag

[JonB_in_Glencoe]

Jon that fallacy that they can't fire unlocked should read highly unlikely but I had a 223 do that not to the catastrophic result you had but enough to shake my faith in absolutes case ruptured on down side gas went in the mag

Oh, this wasn't mine or anyone I know personally, it was just a fella on facebook. I posted to start a conversation.

[Char-Gar]

Move along here, nothing to see. Just another irresponsible handloader should not be allow around a loading press.

[NavyVet1959]

I've had ONE slam-fire with an AR and it was inside my reloading "shack". I still have the hole in the carpet and dimple in the concrete to prove it. No damage to the brass though.

[bruce drake]

Hey! I use the same load in 296 my 30-223Rem with those Z-Max bullets! Its a good load. I could possibly add a grain more powder but why when its effective and accurate.

[Yodogsandman]

High primer? Dirty bolt? Crudded up chamber? Soft primer? Minimal sizing? Thick neck?

[popper]

Yup, any of those + dirty FP, lots of reasons. Yes, slam fire of 308W near max load with cast boolit will take out a BIG chunk of concrete. Shoulder just a tad too long. Yes, it disintegrated but the GC didn't. Case gauge is your buddy.

[JonB_in_Glencoe]

one of the photos of the disassembled BCG

the poster states...

The firing pin does have a little weird corrosion on it. That's not carbon.

[Hamish]

Ah, now we're getting somewhere,,,,,,,

[Tackleberry41]

Hamish, I assume tackleberry's fella who was sizing down 311 bullets (probably CB) to fit 300BO, is a different fella than the fella I posted about.
==========

I posted the OP, cause I thought it was a chance that it was a S.E.E.. Possibly caused by wrong primer/poor ignition. But after more, continue discussion on FB, it seems more likely to be a firing out-of-battery issue, as the owner, when asked, claims all the locking lugs on the bolt look good, and the lugs inside the barrel extension 'feel' good.

No this guy wasnt sizing cast .311 down to .308. He was sizing jacketed .311 AK bullets to .308. Told him to stop, use a bullet puller, but he was determined to burn thru what he had 'for the brass'. He works in a gun shop.

My friend wont use a cast bullet in ANYTHING, even tho the 300BO really seems to like cast. He gave me a box of the Lee 230gr, the same guy had cast them. Not one was actually .308 much less .309. It was free lead to toss in the pot.

[mcdaniel.mac]

I saw an OOB once on an AR. The dingleberry decided that the floating firing pin scared him, so he added a spring to keep it from dimpling primers during cycling, then added a stronger hammer spring to fix the light strikes. Eventually the spring broke and jammed the firing pin forward resulting in a quick 3-round burst that ended with an OOB and a bullet stuck in the bore.

He's the sort of fella who sports a scar on his palm, courtesy of his own handgun. Let's just say he's slightly more diligent about clearing the chamber these days.