Seperate from the video I also have dedicated mags for 300 blackout and nothing else. Unless you never take both ammos to a range, they never escape your ammo cans during storage and clean up, dedicated mags for 300 won't save you. I think I cross contaminated my 556 can while cleaning up loose 556 on my storage shelf. I could keep things cleaner and I think a little sloppiness got me.

This was one of my concerns that kept me away from .300 for a long time. I recently got into it because I am starting to reload .223 and .308. I am keeping the .300 in seperate cans, separate closet, and I'm only using Aluminum mags for it. I guess I need to also be extra careful when loading mags and make sure all the .300blk is accounted for.

One thing I am concerned about is using gear like chest rigs and belts with loaded .300 mags. I'm thinking only take one caliber to the range at a time. Visibly and physically clear out all gear before going to range. Take loaded mags, load gear, shoot. Clear out equipment before leaving.

This is something I worried about when I built my 300. With psa’s prices I only use red or black tipped 300. All ammo stays in the box no lose rounds. Anything loaded goes exclusively into tan lancers.

Complacency got me. I've got 2 300 blk rifles. I reload for them and I built my first one in 2014ish I think. Never happened before and became complacent with ammo storage.

Glad youre  ok OP!!!

What I do.

I load my mags at home with a speed loader from caldwell.  Put the rounds in a load block, I can see whats going in the mag before hand. I take my time,  and all my mags are marked and separated.

I keep 50 cal. cans full of loaded mags. This is my habit as when I go to shoot, I want to shoot, not load mags.

This habit has a secondary benefit of minimizing the risk of what OP had happen since when I'm loading mags, ONLY the type of ammo I'm loading is out.

I load new ammo, straight from the box, into the mags. Mags into cans and closed up making sure the label on the can is correct.

BO mags are all smoke Lancers with bands as well. NO Lancers with anything but BO in them and NOTHING banded but the Lancers.

I have some go bags that have both calibers in them as well as 9 and 10mm mags. The .556 mags in these are all USGI metal mags so you can tell immediately by the feel what's what. These bags are OD and have more .556 in them. There is also one that is black and it has more BO. It's mine and my tribe all knows this. If things ever do get serious, I'll have the only BO. Not ultra safe like this but I wanted a bag that had some of whatever I may have available ready to go on short notice.

Is it perfect? Nope but hopefully it makes it much less likely to have a mix-up.

Glad OP is OK.

After enough of these post I sold all my 300BO ammo and swapped the AR 300 barrel for a 350 Legend.

Glad you're ok OP.

I will be adopting several of the practices others have mentioned here. I appreciate all the well wishes.

I hope this post helps others avoid a similar event.

You ever try shooting a 308 in a 270?

Nope - because I don't own either.  There is a bazillion rounds out there, of course it's possible to find one that can mischamber. But you have to look and they try to minimize that.   Fortunately the numbers of people who own both a .270 and a .308 is a tiny fraction of those who own .300 and 5.56.   And fire a total on average of like 20 rounds a year.

Unlike  300 BO which is a round that specifically caters to people who all own 5.56 guns, and fire thousands of rounds a year at a high rate,  often intermingled.  When's the last time we've seen a 308/270 kaboom?  Also,
308 rounds ARE notably shorter.  A .300 BO has thr same AOL and fills the 5.56 magazine the same, where a .308 is shorter than a .270 mag.  you can still fuck it up, ot is an issue,  - but by the numbers, it's not happening hardly at all, for that combination of reasons.   And since when is "oh that fuck up can happen under these other conditions, so it's OK, don't worry about it", a sound safety philosophy?   But to your point - no, I would not own both.  Just like I don't own a .300 BO, but went Grendel.

Fwiw I agree with the potential danger of the 556/300 issue but disagree with you down playing the danger of other potential dangerous combinations. Especially extremely common cartridges that have been around much longer.

I'm curious now if a 7x57 could fit in a 270. I just tried and a 308 won't fit in a 7x57.

300BO as it was done was bad from the beginning. Great idea. Botched execution.

That sucks man, glad you are OK.  Guns can be rebuilt.
Complacency can get all of us.  
Luckily, I'm on the opposite end.  I don't shoot 5.56 anymore, so it isn't a concern (for me).  

But if I ever take my 5.56 to the range, I will triple check every round I load (I already have a few pre-loaded mags that have been sitting around long before I even got into 300blk).

Oh you are right - and don't let me downplay that at all.  I will do everything I can to not own a possible Kaboom combination.  Fortunately there aren't many (for a reason), but it's not completely impossible.  .308/.270 is a good example.  7x57 in a 270 is another, but fortunately those numbers are pretty small, and so related kabooms are rare - but yes, the point remains - you are quite right.  

Also, don't put yellow shells in your 12 GA!  (If you didn't know, all 20ga ammo is yellow.  All of it, always - for this reason, and no 12 ga ammo is yellow - ever).

Had a customer who tried.  Fortunately his son had bought him an inexpensive push-feed action, so it just went click.  He was PISSED.  I talked him down, "University" took the rifle back, and I sold him a more expensive rifle.  

this

the day I finished assembling my first 300blk I failed to have any inert snap caps lying around and used live rounds for chambering and ejecting function check.  stupid.  

no, the obvious Bad Thing did not happen.

what did happen was that I picked up the 5.56 identical looking rifle I had assembled the week or so earlier and cycled the 300blk through it.  then my blood ran cold when I realized what I had just done.  I immediately changed my plans, put different furniture on the 5.56 right then and there, and decided that all unique ammo should be in physically different shape/material magazines.  and I load them directly from manufacturers boxes not bulk packs.  more expensive I know.  

so 300blk is in pmag30

5.56 is in pmag40, the $2/rd premium ammo is in pmag10.  

6.8 spc is in C-Products 26rd dura-mags.  

when I eventually end up with 350 legend they will probably get pmag20.  224 valkyrie will be in 20rd dura mags.  

if I add more calibers they will all get their own fundamentally different magazines.  I'll probably run out of spare time and disposable income before I run out of unique magazine options.

that statement is provably false.  did it myself once.  please don't post that again.



you obviously do not have any experience with 300blk, ar platform, and should not be giving advice on either topic.  

eta: if all your experience with 300blk is subs, don't assume everyone else shoots subs 100% of the time.  if someone actually listens to you without realizing you left out a critical detail (subs vs supers) your comments could literally result in a kaboom.  leaving my original response as is.  

I have been suggesting clear mags for 5.56 to .300 Blackout shooters for some time.

You can force it to chamber a variety of rounds in the AR platform. I have seen a 243 get chambered. In theory, it should not, but if you have ever met a redneck, anything is possible.

There are lots of videos out there of guys easily chambering a 300 in a 5.56 barrel and blowing them up, for science.

OP, you and your family and not injured and that is what matters. Stuff is just stuff and easily replaced

I'm going to avoid comment other than to say glad you are OK.

Pricy lesson.

This.  Bad day for sure but could have been a lot worse.

Thanks for sharing OP

Glad you're ok, OP.
I also applaud you for posting this, it sounds like you're owning it, have fixed the rifle, so none of this next part is dumping on you specifically.  In the end, we all make mistakes one way or the other.

300blk is by far, in my opinion, the best and most viable SBR round because of it's interoperability with 5.56.  I've owned 300blks since almost the beginning of the cartridge, and just in the last couple years I see it is becoming trendy to blame the cartridge for people blowing guns up.
Blaming the gun or the cartridge is total bullshit.

All you have to do, as with anything else regarding firearms, its take some basic precautions, and pay some basic attention to what you are doing.  Sounds like the OP wasn't doing that, due in part to wearing NV stuff. (is that an excuse, are we blaming the NV?)
Pay attention to loading mags.  If you are paying enough attention to stick them in bullets forward, you can see that this one has a bullet three times bigger than this other one.  It isn't that hard.  Yes, I would notice this 100% of the time, because the amount of attention needed to get the round into the mag correctly should absolutely be sufficient to get the right ammo in the mag.

For me, they sit right next to each other in identical looking boxes in the closet and I think nothing of it.

In my case, the guns are configured differently, so I never have to wonder about which gun I have in hand; I know instantly which of my guns are 300blk by looking at them from any angle.  That helps.
I also mark the mags with a bold "300".  That helps.
This isn't exactly why, but I typically don't have them out of the bag to shoot at the same time... that helps I guess.

At the end of the day, you are responsible to pay attention to what you are doing and not blame correctly functioning equipment.  Look at the ammo you are putting in the gun to make sure it is correct.  Easy and basic.

It seems the NV equipment keeps you from focusing close, is it the NV's fault you blew up a gun?
Hodgdon sells Titegroup that can be easily stuffed in a .308 case, is it Hodgdon's fault you filleted a gun?
I've also got 308 and 6.5 creed that use the same mags, both go in ARs.  I don't know which chambers in the other because I pay attention to what I'm doing, but if I blow one up from putting the wrong ammo in it, which ammo is at fault?  None.  It was me.
Same for 300blk.

If you think you can't put the right ammo in the right gun and don't want a 300blk as a result, you are probably right.  But, you need to take a long hard look at your attention level with firearms, and get better.

As far as whether 300blk will chamber in 5.56, it is entirely dependent on the bullet profile and OAL; some will, some won't.
I was standing there as the RO at a local outlaw rifle match years ago, long before people started blaming the ammo, with a guy there happily firing away with with his 5.56.  Halfway through the mag, he gets a click. Rack, click, rack... about that time I noticed they were 300blk rounds landing on the ground.
He voluntarily packed and left for the day as I recall.  That day the firearm gods smiled and spared him.  Hopefully a lesson learned.

Another anecdote; the only gun I've had blow un in my hands was a 300blk, loaded with factory remanfucatured 300blk ammo.  It was cooked worse than the OP's... looked about the same except the lower around the magwell was bulged and cracked too, and the mag was blown all the way out.  I never knew what went wrong and the ammo company paid to replace it.  I'm surprised the OP's gun doesn't look a lot worse actually.

Again OP, glad you are OK and good on you for having the stones to own it.

One of my buddies laughed when I bought these...

Bands

I said if it saves me one rifle or picking metal out of my face I'm about $500 ahead.

I put one one the stock and one on every magazine.

I bought something similar yesterday based on some of the replies in this thread. I will keep shooting 300 blk. I'll keep shooting 5.56 and both under NVGs. I am also going to adjust how I do things especially at night.

I am going to switch my clear mags over to 556 and my black mags to 300blk.

Just makes more sense to visually make sure a 300 round isn't in a 556 mag.

I will need to buy a lot more lancers cause i will have 50 mags for my one 300blk gun and only 10 mags for all my 556 guns.

I'll be buying 6-7 of the transparent Magpul mags when they come out in a few months.

This isn't fool proof but I only load 300 into aluminum mags, as I only have 2 (300 rifles) and they have gold Shot show magpul loop things on them.  All my 556 mags are pmags.  This doesn't prevent me from loading the wrong ammo in the wrong mag but it helps me identify which magazine should have the correct cartridge.  A guy on my local forum had a bunch of those livestrong type of bracelets made that say 300 blackout or something and gives them out.

forgot to tell OP a huge THANK YOU for posting.  

let's keep this thread towards the top of the forum for a while, see if we can reduce the frequency of this kind of thing.  

"days since last 300blk kaboomed a 5.56" counter suggestion?  as a sticky?

That would be good.

Interestingly, there never seemed to be any reports of .300 Whisper blowing up guns, though I suspect the relative obscurity of the round and that it was primarily chambered in T/C Contenders to be the reasons why.

I've never found a use for 223/556 in my area but have found 300BLK very useful. I'd be happy to get into the weeds on this but its not relevant to the conversation at hand.  Been beaten to death in other threads.

I do shoot with friends who run 223/556 and because of that I only use red aluminum mags for 300 supers and the clear Lancers for 300 subs.   No one I know runs red mags, and although the Lancers are not uncommon, they are the exception with my 223/556 using friends.  This helps.  We try to keep our mags to ourselves but inevitably they get mixed up on the tailgate of the truck.

Now, I do have a Mini-14 (because it was my father-in-laws, and its cool), but the main point here is that Mini-14 mags don't work in AR style rifles so I focus on keeping the Mini-14 mags in the only 223 ammo box that I own to reduce any cross contamination.

This won't work for a lot of folks but I wanted to throw it out there.

I did buy the goofy bands,and felt a bit foolish, but they are a good secondary level of safety.  I do own some black AR mags and they sport the bands, though they are relegated to long term storage to keep black mags out of circulation.

Stuff like this keeps me from buying anything in .300 BO. I did once shoot a 223 out of a FAL

It sounded off, the action didn't cycle. I worked tbe bolt, a very blown out 223 case elected. Don't think I hit the target either

I shoot both calibers together and often (yesterday in fact). I am careful to not let this happen but this post is just a reminder to be more careful. Thanks for sharing.
Glad you are ok.  

If you don't care about subs 300 Hamr won't chamber in a 556

I sent my brother off one weekend w/ a new to me Type 99 & some 6.5 Jap I had left over from my last Japanese rifle.

Now he won't test fire my guns no more.  

heh.  there's a table full of 300 whisper at the Fun and Feather in Iowa City with peel and stick labels saying they will fire safely in 300blk rifles.  

but the price is higher than the current factory loads for 300blk subs.

I had money to spend, Wilson had the exact 300 hamr barrel I had chosen on sale, I added it to my cart, it wouldn't let me buy it because they only sell to FFL.  

wtf?

fuck that.  

I was ready to buy into that caliber until the chat asshole was snarky with me.  

if Wilson doesn't want my money I'm ok with that.  more money to spend on 6.8 spc which still has more support in the industry than 300 hamr. muzzle energy is about the same.  no functional reason for me to buy into another caliber.

That place is clown world.

Because of this thread i now load 300blk in magpuls, and 5.56 in clear Lancers.

The mags look different, feel different, and I can visually check the rounds loaded into the 5.56 mags.

you reassure me that I have contributed to one positive change in the world this week.  

it's been a hell of a week.

I know how many stupid things I've done in the past, I try to figure out how to prevent doing a future stupid thing.

This is why all my 5.56 mags are now translucent Lancers, easy to do a visual inspection when loading, when pulling from storage and just before insertion.

But no system is perfect cause we're not perfect.

You can take all proper precautions and still have a kaboom, they've been happening long before ,300bo ever came out.

Glad the OP shared this, we've all made mistakes and sometimes the consequences aren't small. But gun parts are still cheaper than body parts.

And wear your safety gear...

This dude put a 300 thru a 5.56 barrel. Not successfully thou.

Well - it successfully exited the barrel.  But most of the gun was toast, including a bent magwell.

Same.

The only reason to own one is subsonics, and 9mm does that better IMO.

Bought a few Wilson barrels.  No FFL needed.

The supersonic rounds in sub 7" setups work very well and are superior to 5.56 in that size. They'll also hit harder than 9mm from the equivalent size barrel.

The 300blk is the ideal mainstream PDW round.

I should've clarified, the only reason I would want to own one is subsonics, and 9mm does that better.

I'm perfectly content with my 11.5in SBR in 5.56 for any HD use and I don't need or want anything shorter for true social work. Building a 9mm upper at the moment for subsonic fun and pest control.

The cost of setting up to reload for 300 Blk, not to mention the hazard of potential KB's, makes it not worth it to me.

This. Thanks OP, glad you're okay. People need to see this kind of stuff and know it can happen.

.300 Blackout subs have superior external ballistics to 9x19mm, certainly.  Much higher BC.  Do they have superior terminal ballistics?

ETA:  Ah, you were talking about supers.  6.5 Grendel, 6.8 SPC, & 7.62x39mm supers all do better from a shorter barrel than 5.56.

Meh, I'm not sure a 77gr tmk is going to be substantially different. Plus I don't have to worry about blowing up my guns plus they're lighter for carrying all day.

I had weighed them before.

A 77gr SMK (IMI) and a 110gr Hornady V-max were just about the same weight on my kitchen scale.  110gr Tac-tx was a hair heavier, but not much.   I may have to go back and re-record how much their exact weight.