Sanity check me - 300 BO Kaboom from reload

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JStarX7
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Sanity check me - 300 BO Kaboom from reload

Post by JStarX7 » Sun Dec 06, 2020 1:00 am

Long story - short as I can make it version:

Loaded up 20 test rounds of 300 BO. Done over 2 night, 10 rounds a night.
220gr Hard cast hi-tek coated bullets
Accurate #9 - 8.3gr
OAL 2.17 (Mostly, the bullets vary - some are very rounded, some are a bit flat on the nose, but the die seats them at the same depth.)

My process is such that all my finished brass (which I include priming in) is in an ammo box, I pull X cases and load them one at a time with a charge. While my CHargemaster lite is counting the next charge, I put a bullet on and put the round in the press. Once the next charge is counted (I wait, because sometimes the press moving will mess up the powder trickle) I seat the bullet/crimp. Put that round back, grab the next case, charge it, put a bullet on, put it on the press. So on an so forth. My reasoning is that by never having a case with a charge without a bullet, I can't double charge. It's hard to put a second charge in if the mouth is blocked by the projectile.

Today: Loaded Magpul M2 into rifle; 10 rounds from last night were on top. Fired 5 without a suppressor, just to make sure they weren't going to keyhole or something that might mess up my suppressor. No issues. I mean, they don't load the next round, but these are subsonic rounds so that is to be expected sans-suppressor. Chrono-ed all rounds. Between 1030-1045. Perfect!

Dropped the mag, checked the chamber. Screwed on Silencerco Omega 300. 4 rounds, good. 1045, 1038, 948 (Weird, but ok...?) and 1053. Next round KABOOM! Blew the mag out. Round was very loud, big cloud from the ejection port. My rifle is pretty much F-ed. The lower looks OK, but the BHO broke. The mag button was popped out, but it popped right back in. Hoping it's good, as it's my registered SBR.

Upper? Can't eject the round. Bolt is 90% closed, will not open. It looks like the upper receiver is bulged around the bolt slightly. Looked down barrel with flashlight. I can see straight down to the bottom of the case.

Despite my care, this appears to be a double charge, right? I would have thought maybe a squib, but even the weird slow round registered on my chrono. If I shot and nothing registered on the chrono, I would stop. I caught a factory squib earlier this year just from the lack of recoil, but this felt normal until the kaboom.

I plan to get a new upper and BCG. Hopefully the charging handle can be salvaged. I still want to reload 300 BO, so I want to make as sure as I can that nothing else could have caused that kind of pressure spike.

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Regaj
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Re: Sanity check me - 300 BO Kaboom from reload

Post by Regaj » Sun Dec 06, 2020 8:47 am

A double-charge or a squib are the two things that instantly come to mind with a catastrophic event like you had. You've obviously considered both those, so it's hard to say. But it is true that we often misremember or misconstrue "facts" in the netherworld of our memory, after the fact. As countless self-defense shootings, car accidents, and similar anxiety-filled moments will attest.

You don't mention the primer you used. Different brands - and certainly different types - of primers can have a significant effect on pressure... though generally not enough to go from okay to catastrophic in one fell swoop. Still, I'm not a fan of pre-priming brass for that reason... It's too easy to misremember what you put in there.

You also don't mention the brass you used. Was it mixed? What was its history? Brass can have considerable variation - headstamp to headstamp - in terms of its thickness and resulting capacity. That can mean major differences in pressure.

Likewise the bullets. What was their provenance? If one was sized incorrectly you would see a sudden spike in pressure. Did you slug your bore before running those bullets? Even with good bullets, of proper size, from a reputable maker... I would not shoot lead bullets through a suppressor.

The last red flag to me is your loading 20 rounds over two nights. Twenty rounds isn't much, and doesn't take long... and so that suggests that perhaps you were hurried, or interrupted? Successful handloading is about attention to detail, as much as anything else. Doing a little bit here and little bit there is a recipe for making a mistake.

Sounds like you've got some unfired rounds from that batch. If nothing else I would pull each, carefully weigh each charge, and mic each bullet.

Sorry to hear of your misfortune. But glad it was only the rifle that came a cropper.

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dellet
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Re: Sanity check me - 300 BO Kaboom from reload

Post by dellet » Sun Dec 06, 2020 1:01 pm

300 Blackout, not just for sub-sonics.

JStarX7
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Re: Sanity check me - 300 BO Kaboom from reload

Post by JStarX7 » Sun Dec 06, 2020 1:49 pm

dellet wrote:
Sun Dec 06, 2020 1:01 pm
Sounds familiar
[img]<a class="vglnk" href="http://yoursmiles.org/msmile/think/m1708.gif[/img" rel="nofollow"><span>http</span><span>://</span><span>yoursmiles</span><span>.</span><span>org</span><span>/</span><span>msmile</span><span>/</span><span>think</span><span>/</span><span>m1708</span><span>.</span><span>gif</span><span>[/</span><span>img</span></a>]

<a class="vglnk" href="viewtopic.php?f=141&t=97062&hilit=Loading+distractions" rel="nofollow"><span>http</span><span>://</span><span>www</span><span>.</span><span>300blktalk</span><span>.</span><span>com</span><span>/</span><span>forum</span><span>/</span><span>viewtopic</span><span>.</span><span>php</span><span>?</span><span>f</span><span>=</span><span>141</span><span>&</span><span>t</span><span>=</span><span>97062</span><span>&</span><span>hilit</span><span>=</span><span>Loading</span><span>+</span><span>distractions</span></a>
Ah, yes. That does look like it.

popper
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Re: Sanity check me - 300 BO Kaboom from reload

Post by popper » Thu Dec 10, 2020 9:49 pm

A small cycle tire tool will get the bolt open. Never used #9 but seating depth will change pressure. Ar case head is not fully supported. IMHO your flat nose vs pointy nose and seating depth is problem.

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dellet
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Re: Sanity check me - 300 BO Kaboom from reload

Post by dellet » Fri Dec 11, 2020 1:20 am

popper wrote:
Thu Dec 10, 2020 9:49 pm
A small cycle tire tool will get the bolt open. Never used #9 but seating depth will change pressure. Ar case head is not fully supported. IMHO your flat nose vs pointy nose and seating depth is problem.
Always possible, but not likely here.

10 rounds of the same load without an issue, and that load will probably max out around 12 grains. Velocity would have been 1300+.

If a bullet was beat into the case due to recoil in the magazine, It could happen. More likely if it was a seating depth problem it was too long and jammed into the lands, but again one round out of 10 does not make sense.
300 Blackout, not just for sub-sonics.

JStarX7
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Re: Sanity check me - 300 BO Kaboom from reload

Post by JStarX7 » Fri Dec 11, 2020 1:52 am

Just reviewed the video footage. Was actually the 11th round, so a round I loaded the first night. (After the first night, I decided I wanted 20 total rounds to test, which is why I did 10 more the next night.)

Chrony picked the round up at 1053 as the round detonated. I would think the round would be going faster with a double charge, but it could be that so much of the force was sent back through the ejection port and mag well that it didn't really affect the velocity of the bullet down the barrel. The suppressed rounds sound like movie shots in my GoPro, except that 11th round, which sounds like a very loud rifle shot.

I haven't had a lot of time, but I did try to pull the rifle apart. The bolt is stuck fast. I've tried a few things to get it out, but it is not budging. I may just have to cut the receiver, since I want to recover my Geiselle charging handle and the Troy back up sight. I'm going to try to remove the barrel nut to see if I can pull it, but I think the bolt is holding the chamber in place as much as the chamber is holding the bolt in place.

BJK
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Re: Sanity check me - 300 BO Kaboom from reload

Post by BJK » Fri Dec 11, 2020 9:38 am

That's the pits. It has me re-examining my load procedures and for us, that's all we can get out of it. For you it's just the pits.

Frankly the potential is there for a double charge can happen no matter how I load. If I load on the progressive press if something happens in the load process I can get a double charge, but generally I know that's a possibility and address it. If I'm on the single stage press I get around that by using a loading block and drop all the powder charges one right after the other while they're in the loading block. Then I eyeball every case before seating the bullet.

popper
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Re: Sanity check me - 300 BO Kaboom from reload

Post by popper » Fri Dec 11, 2020 11:28 pm

Get the small tire tool and lever against the upper forward mount lug. It will come out. If the nose is too large it might jam and increase pressure or a deep seated bulet. May have just blown the base off and jammed, no damage to the upper.

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dellet
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Re: Sanity check me - 300 BO Kaboom from reload

Post by dellet » Sat Dec 12, 2020 11:35 am

Try to drive the bolt forward first then back out.

The locking lugs need release from the barrel extension and the cam pin might have rotated slightly.

With any luck the case separated and you won’t be fighting that also as the case needs to twist.

The worst part is he flinch you will have every time you pull the trigger for the next 2 years :lol:
300 Blackout, not just for sub-sonics.

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