Sure.   all sounds good.

Though - one common trend with most .300 BO Kabooms is pretty much exactly that description.  It's preceded by pretty much that entire discussion and description, and carefully marked magazines and management and certain observation of every round loaded and handled.  And an OP who of course is very careful and he himself could never actually miss one.  

And then a rifle blows up.

Not everybody.  99+% rifles don't.  Good practices increase your odds of being on the good side of that.  But smart attentive people with separation systems, who run .300 BO, still sometimes blow up.  I don't cast judgement, I accept that it's part of being human, to make human errors.  The only eye-roll I have is the unwillingness people have to recognize that their own attention spans are not what they actually think they are - which we get reminded of again and again.  And people mock and say the guy just didn't pay attention - which fortunately nobody did here on this one with good tact here in a tech forum.  But if this had been a random Youtube video drop of a guy who blew up an AR with .300 BO, that someone just posted as a video found; people would have ripped that operator to shreds.  People do that without recognizing they too are The Guy, who sometimes didn't pay attention - every day; and don't know it.   And the best way to fix that, is systemization.  Good housekeeping practices and so forth certainly help.  But the best systemization to avoid a .300 BO induced Kaboom, is to not have .300 BO.  

I'm not the boss of you - I'm just some jerk on the internet talking.  But yea, that is the decision a lot of people make is to just not get .300 BO at all.  Because for those who aren't running an SBR with Subsonics with a Federal NFA ATF Registered suppressor, the .300 BO offering spectrum of differentiating advantages list gets real short real quick.  And if suppressed is the goal, there are other options.  230 gr .45 ACP at high end subsonic out of an 8" BBL with suppressor being one route; amongst many.  The advantage of going from supersonic to subsonic same-gun, is a perceived advantage I don't share the value - considering the sights are going to be pretty off between those two.  That, and  I don't know anybody with a .300 BO who doesn't also have and bring a real supersonic rifle every time anyway.

That list and practice is a good start, and this is a good thread to talk about risk-mitigation practices.  Apologies in advance for kind of being a jerk here.  That stuff helps.  Just be aware that OP thought he had that down too.  And props to OP for having the willingness to start this thread.  I can only guess how many times others chose to not; but by word of mouth and other routes - this happens more often then you see people coming in here and posting about it.  The good news is the AR15 is designed to safely fail in a manner that a catastrophic overpressure and explosion only results in property damage, and really, not that meaningful, since for most people these guys are discretionary toys purchased after the rest of life's expenses have been covered.  It's an affordable loss that when mismanaged doesn't physically harm the operator usually.  

As always, it's OK to like stuff I don't like - and to enjoy it.  Being this is the AR Technical forum discussion, that's my own technical opinion on the topic.

I'm not trying to be inflammatory. But owning 300 and 556 is no more risky than say, reloading. Where a slip in attention span can cause a double charge and kaboom.

The problem I have with your line of reasoning is it also excuses negligent discharges. "Smart attentive people sometimes have them" and "its part of being human making mistakes". I just don't agree with that.

Like I mentioned before. Not knowing whether your gun is loaded and accidentally chambering 300 are caused by the same problem. Complacency. Which is always dangerous with firearms no matter what you are doing.

That said if you can't trust yourself to keep it straight and aren't willing to take the precautions then don't risk your safety by owning a 300 black. I'd say the same thing to a person who can't trust themselves to reload safetly. Or can't trust themselves not to have NDs. Their safest bet would be not owning guns.

Is it a lapse in engineering judgement? Yeah I'll give you that. However their goal was as much parts commonality to 556 as possible, which had the unfortunate side affect that we see now.

I appreciate OP showing us what happened and I'm sure it was a real eye opener for him. Scary experience having a gun blow up. Glad he is OK.

The safest AR you can have is anything other than a 5.56 - including a .300 Blackout.  The danger comes when YOU have a 5.56 and you have a .300 Blackout - or one of your shooting buddies has one.

"I'm out!  See you guys next week."

"Here, I've got an extra loaded mag..."

No firestorm all good.

I will say, one difference is Reloading isn't for everybody.   And is a known elevated risk practice.  .300 BO is sold and promoted like it is for everybody, and is just another gun and suitable for everybody sitting right next to their identicle 5.56 gun.  And on the wide retail level is placed and managed like there are no additional special additional safety consideration.

Everyone says "same as reloading".  Not really - reloading stopped being number 1 cause of 5.56 kabooms a while ago.  One factor is reloading is not done under dynamic field conditions.  Nobody is wearing night vision fishing reloading components out of the can while the wind is blowing.  Or spilling ammunition in the field and grabbing magazines.  Field conditions and what details have your attention are very different than at home on your reloading bench in controlled conditions at your own pace.

300blk is a great round for AR-15 IMO

My only 300blk is bolt action so this doesn't occur

Glad you are ok OP

You're not going to blow up your bolt action.  How many 5.56 semi-autos do you own?

This is an example of the complacent thinking that leads to accidents - I put all my .300 Blackouts in clear mags so I won't get them mixed up.  I put bands on my .300 Blackout mags so I can tell em apart in the dark.

You're probably not going to fuck up w/ an entire mag - just the weight of the loaded mag is different.  It's the single loose round that makes it into a 5.56 mag that blows up guns.

If you have clear mags, put all your 5.56 in the clear mags so you can visually see if a single .300 round got in there by mistake.

It was a 300 Blackout 147GR FMJ remanufacture from Capital Armory.  Bought 300 rounds of bulk from them last year.

There are other calibers that have the same problem as .300 Blackout and 5.56. Safe ammunition storage practices and safe firearm handling/use are important at all times.

You clearly misunderstood

I don't have 300BLK in ar platform so accidents like this don't happen
if it's going in the bolt gun it gets checked and all 300blk is only out with the bolt gun

Thanks, OP
So non-ballistic tipped brass with a brass case?
And if bulk, I'm assuming they came loose instead of in 20 or 30 round boxes?  
 

BTW, I'm not trying to criticize or second guess, I'm trying to backtrack into how we can all prevent the bigger issue, which is cross contamination.   I can have all the mag-bands on uppers and mags in the world, but that won't do me any good if I think I pulling from a bulk 5.56 stash, and there is a 300 danger noodle lurking in there.   Unless I am paying 1000% attention and in bright light, a brass/brass FMJ could slip by, and that is real danger.

I don't have any bulk (loose) 5.56, but I do have multiple varieties of bulk 300blk, and one of those are indeed, non-ballistic tipped, brass/brass rounds.  Luckily, they are the Remington 220gr, so they are quite a bit heavier that 5.56 rounds, but that is still a potential mix-up point.  That is something for me to keep in mind.


I think the new TMAG's are going to help a lot as well.  Use TMAG's for 5.56, and Lancers for 300blk, although that won't help this particular situation (loading from bulk at night).


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Since I 'm not actively shooting 5.56, I currently have a 0% chance of a danger noodle.  But because I (and most other folks) still own 5.56 ammo's and uppers, I need to stay on top of things, and do everything I can to mitigate potential problems.  

Sorry for your troubles OP, but I'm going to use this as a lessons learned and update my best practices with these opportunities for improvement.  (Gotta love review time at work).

With a cross frequency of having both at about 1/10th and a round count rate of about 1/100 in comparison - but sure.  And examples of other unsafe scenarios is not justification of dismissal of an unsafe scenario - particularly one with a wildly higher kaboom rate.   I doubt 10 rounds ofb.270 a year are fired combined of everyone I know who has a .270.  None of which use the same mags as .308

Only load it in clear Lancer mags with a 300 BLACKOUT band around the base.
Funny how 300 BO can chamber in a 5.56 barrel but not the other way around as this would e safer, a .223 bullet going down a .30 cal barrel.

Excellent advise.  Which is why I don't have any ammunition or firearms that can be mischambered in any other firearm I have and Kaboom.   For example, .300 Blackout.

I completely respect that.

There is a Paradigm shift for you.
But since that is not likely to happen anytime soon, just like 300blk is not likely to go away, what else can you contribute?

I think it needs to be the opposite (load 5.56 rounds in clear mags so that a 300blk round can be spotted), which is why I think the TMAGS will be helpful.

I'll put my 300blk in my Lancers, and outside of my D60, any 5.56 will go in TMAGS.  Will still use mag bands on the uppers and mags.

I'll also make a continued effort to shoot 300blk rounds that have ballistic tips or different shell casings.  Off the top of my head, these rounds have ballistic tips or different cases:

110gr/120gr Tac-tx: Black tip except for some of Black Hills (military) that had Brown tips
110gr Varmageddon:  Black tips
110gr V-Max: Red tips (or green or black)
110gr AAC Sabre: Black tips
120gr Sig SBR: Black case  (Note: The 120gr HT version is basically the same round, but has a brass colored case instead of black.  I have both versions.)
125gr Nosler Ballistic Tips: Green tips  (May have to deep six my 5.56 green tips, which I can't shoot anywhere anyway)
125gr SST: Blue tips (or red tips)
144gr FMJ (Aussie): Black case
147gr FMJ Wolf Steel: Grey case (This ammo does not work in PMAGs, but does work in Lancers, which is another reason to use this mag for 300blk)
190gr Sub-X: Red tip
208gr Amax: Red tip
220gr AAC Sabre: Black tip

Not quite as worried about subs chambering or getting mixed up, but will still need to be careful. Especially with subs that are not ballistic tipped or don't have different color casings.

No, I understood all right.  .300 Blackout guns DON'T blow up.  It's the ARs in 5.56 that do.  How many ARs in 5.56 do you have?

If it's going in the bolt gun, it doesn't matter.  Either the bolt won't close, or it'll go fut & rattle down the bore.

It's WHEN IT'S GOING INTO THE 5.56 AR that it MUST BE CHECKED.

That's actually valid.  If you run .300 BO and have NO 5.56 guns, that is actually equally as safe.   It's really rare, but equally as safe to go that road.

Au contraire.  .308 will absolutely go into a .270 magazine, and chamber.  The only reason my customer didn't blow up his .270 w/ a .308 round was his son was on a limited budget and bought a push-feed bolt action for him instead of a controlled round feed action.  Click and the .308 had to be rodded out of the chamber.  I calmed him down and sold him a more expensive .308.    Lessons here are:  never buy a gun from a shoe salesman even if it's a bargain, and always check the caliber marked on the barrel.

It's safer to have no 5.56 guns and any number of .300 Blackout guns than the other way round, b/c .300 Blackout exists.

No disrespect meant, and I’m not trying to hijack this thread, but I do find it interesting how much better a geissele super duty held up to a 300 blackout in a 5.56 chamber.

With the geissele they pushed the bullet out and the rifle was still functional.

Wish I could find the archived thread.