R.I.P. One AR-15 Rifle – Another 300 Blackout / .223 Kaboom

I’ve read a few stories recently about someone, somewhere, shoving a 300 AAC Blackout cartridge into a .223 / 5.56mm rifle and pulling the trigger – subsequently blowing their gun to bits. Some folks call BS and say it can’t happen as the rifle won’t go into battery and fire.

Well, I’m a believer now, considering a guy 3 lanes down from me blew up his fairly nice looking AR today. In the confusion, I was not able to get the brand of the rifle, but that matters little. Containing 55,000 pounds per square inch of pressure is not in the job description.

This was the round below the cartridge bomb in the magazine. I found it on the ground amongst lotsa small pieces of magazine, spring and follower. And quite a few case fragments. As you can see, it absorbed some violence.

This was the round below the cartridge bomb in the magazine. I found it on the ground amongst lotsa small pieces of magazine, spring and follower – and quite a few case fragments. As you can see, it absorbed some serious violence.

I was pretty occupied with my own business, gleefully trying out two new SilencerCo silencers for which I’ve waited about 10 months. A 22 Sparrow SS and an Octane 45 by the way. And yes, they’re awesome. Happiness = That feeling when your slide cycling makes more noise than the gun shot. That nirvana was achieved with a Smith & Wesson M&P22 with a SilencerCo Sparrow using Aguila Subsonic 60 grain .22LR ammunition.

Suddenly I heard a “splosion” noise and a scream from a few lanes to my right. Running over to see what happened, I saw a man holding his hand and obviously somewhat shaken up. I immediately started looking at his face as he was somewhat disoriented and all was clear there. His left (support) hand looked like he had fondled a few bricks of charcoal for a while. Thankfully, and maybe miraculously, no cuts or blood anywhere. While his hand was “stinging like crazy” in his words, there did not appear to be any burns of consequence. This is one incredibly lucky guy, especially since I can’t be sure he was wearing shooting glasses. The way they were placed on the table, I’m not sure he had them on when he blew up the rifle.

Here’s the apparent sequence of events, picked up from listening to the rifle owner and the shooter.

The owner had two uppers at the range. A .223 and a 300 AAC Blackout. He obviously hand loads as there were 100 round ammo boxes of each type nearby.

The shooter appeared to be new and somewhat inexperienced. I can’t be sure, that’s just an observation from seeing the interaction after the kaboom. Either the shooter picked up a magazine full of 300 Blackout cartridges, or the rifle owner handed him a magazine loaded with Blackouts. I can’t be sure. They weren’t sure themselves.

The shooter loaded the magazine of 300 Blackouts in the .223, chambered a round, and fired. Then the Kaboom. I was not able to discern, nor was the owner, whether the shooter felt anything abnormal trying to chamber the first round. As  the shooter appeared to be inexperienced, I’m not sure they will ever sort that out.

Once we determined the shooter was physically OK, I wanted to get out of their business, so I didn’t get any photos of the rifle, but I can describe the damage. In short, it was pretty much totaled. Perhaps the Magpul front hand guard, rear stock and trigger group can be salvaged. That’s about it.

Here's a .223 Remington cartridge dropped into a 5.56mm chamber.

Here’s a .223 Remington cartridge dropped into a 5.56mm chamber.

The magazine blew up, along with spring and follower. And you can see what happened to the other rounds in the picture here. I *believe* the fact that he was using a polymer magazine may have saved the shooter from additional injury. The explosion clearly took the path of least resistance. Perhaps a metal magazine would have allowed more pressure to go in other directions in addition to out the magazine well.

The magazine well on the lower was bulged out. Kind of like an Elmer Fudd cartoon shotgun.

The upper receiver was also bulged out from the explosion.

The bolt and carrier were both trashed – bent all to hell and completely stuck in the upper and barrel extension.

I assume the barrel extension and barrel were trashed, but as everything was fused together, there was no way to tell for sure until they rip things apart. Shoving a .308 inch diameter bullet into a .223 inch hole is asking for damage I would think.

While I was not shocked at the damage to the aluminum upper and lower, I was surprised at how much the bolt carrier and bolt were trashed. That’s hard stuff there.

Here's a 125 grain 300 Blackout cartridge dropped into the same 5.56mm chamber. Too close for comfort?

Here’s a 125 grain 300 Blackout cartridge dropped into the same 5.56mm chamber. Too close for comfort?

With the brief opportunity I had to look, that’s about all I could tell. But now I was curious. Would similar rounds allow the .223 rifle to go into battery? I decided to try under much safer conditions.

After removing the bolt and carrier from my Smith & Wesson M&P 15 VTAC (5.56 chamber) I dropped in a .223 Remington round to get a rough visual on where it sat. OK, that worked fine, as expected. Next, I dropped a variety of 300 AAC Blackout loads into the chamber, exerting no pressure at all and just letting the round fall. As expected, the big subsonic rounds didn’t get close to proper depth, however some of the longer and skinnier bullet profiles did – mainly the 110 and 125 grain ballistic tip bullet types. Not to the full and proper depth, but close. Close enough where a little encouragement by an inexperienced shooter could force the bolt into battery.


Wear eye protection. Always. This guy won the lucky human award today and I don’t think that’s given out more than once per lifetime.

When bringing a new shooter to the range, hover over them like a helicopter parent. At least until they gain some knowledge and proficiency.

If you own both rifles, figure out your own method for segregation. Perhaps wrap the Blackout magazines with colored tape, or put a colored base plate on them so they’re easily visible.

It might not be a terrible idea to take one or the other rifles to the range, but not both on the same visit.

Whattdya think?

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  1. Blehtastic says

    I don’t understand why people have multiple uppers for a lower that are not out on some special ops mission in a warzone. The lower is the cheap part of an AR, the upper is where the real money comes into play. Even a high end trigger is the price of a mediocre to low end scope. Unless your hoofing gear miles on end in a warzone and the extra weight is a concern, just get another lower. I plan on addressing this by buying a different color furniture for alternate calibers. I live in Ohio, so FDE is never a good camo choice, but if I get a .300 BLK I’ll have it all in FDE. If I get a 6.8 SPC I’d go with one of those patterned magpul furniture sets.

  2. Chris Brooks says

    Very little sympathy for someone who loads the wrong ammo in their gun. It’s basic “day one” stuff that anybody should be able to figure out.

  3. says

    Fifty years ago, this problem was with people putting 20 gauge shells into 12 gauge guns. The 20 gauge would slip past the chamber, making way for a 12 gauge round, and disaster, at the next shot. It is one of the reasons shotgun shells are color coded. You have to be aware.

    The closest I have come is when I purchased a .257 Roberts improved. You can make the case from 7X57 brass. Somehow, a couple of 7X57 rounds got mixed in with the .257 cartridges that I got with the rifle. It was years before I found them.

    I checked, and with only a little forcing, they could be chambered.

  4. Anonymous says

    I don’t reload my ammo, yet.
    But I learned two valuable lessons yesterday.

    After reading this article just yesterday, I went through the process clearing all my magazines and discovered I had accidentally interspersed 5 Blackout rounds in a magazine full of 5.56. WOW!
    I decided to do a complete quality control inventory of all my other ammo and discovered a few other rounds with BAD PRIMERS. They were in my bulk ammo from Remington.
    Who would have thought.
    From now on I am going “Total Quality Control” with my commercial ammo and never assume anything.
    Thanks guys.
    Again, you may have saved my life.

    • says

      Glad to hear you found it in advance – it can never hurt to “double check”

      What struck me most about this event was the new shooter angle and the need to supervise every single moment. It there are multiple calibers on the table and someone really doesn’t understand all these nuances yet, then bad things can happen.

  5. singlestack says

    Just as when reloading you should only have one powder on the bench at a time, when shooting you should only have one caliber on the firing line at a time.
    With both you should double and triple check before you start.

  6. Kerry says

    The guy at the shooting bench to my left, had a rather nice 30 or 40 year old Bolt Action Sako 22-250, and a box of 50 reloads. He shot about 20 rounds, then took his glasses off to see if the sight picture through the scope was clearer without glasses. Fired a couple more rounds without his glasses, then put his glasses back on and fired another round. This round blew the extractor and ejector out of the bolt, and locked up the action.
    The shooter was bleeding from multiple places on his right check, but his glasses protected his eyes. (At the neighboring shooting bench,my left arm was peppered with what I guess was just powder residue.)

    When the rifle was disassembled, the Range Officer discovered that the bore was clear, but the chamber contained a .204 Ruger Case with a longitudinal split. The shooter said that neither he nor any of his friends owned a .204 Ruger, and he didn’t know how it had got into the box of reloads. (The accident probably only occurred because the Sako is a Controlled feed Action.)

    This was a costly demonstration of how much of the rearward force is normally absorbed by the cartridge case expanding and gripping the wall of the chamber.

  7. PJ says

    In the old Precision Shooting magazine there was a story about someone who did this same thing, except back in those days it was .300 Whisper. He shot a 240gr Matchking in his 5.56 upper. The bullet lodged in the barrel. They drove it out and had a picture of the .308 bullet swaged down to .224 inches. It was very long, as you can imagine…

    I have a .300 WSM and bought some brass at a gun shop from bins and loaded it. After I shot them all I discovered a .300 SAUM case with the shoulders blown forward, that had come out of the .300 WSM bin. Didn’t even notice it when shooting. I suppose it headspaced on the ogive.

    I had a friend who bought a Ruger Blackhawk in .44 Mag (he thought). He bought a box of .44 ammo in the same shop. We went out to shoot it and it was very strange because there was almost no recoil and it was pretty quiet. It wouldn’t even put a hole in the old fence posts we were shooting at, and we discovered we could see the bullets in flight. We finally figured out the dealer had handed him a Blackhawk in .45 LC instead; the .44 rims are the same size so it headspaced properly. Some of the Federal cases were bulged but they all held together…

  8. Jim says

    I have both calibers in different ARs. There isnt much confusion though as they are very disimilar (one is a pistol in FDE, the other mostly black and a rifle). I don’t myself have any problems in recognizing the rounds, but yes a newbie at the range probably shouldn’t be playing with guns & ammo at the same time. I can’t see the owner if they are knowledgable handing over the wrong rounds for their own rifle/pistol.

  9. says

    Doing a little research on the effects of mixing up 300AAC and .223.
    I want to know the outcome of a messup. In a s*** hit the fan scenario when you might have a friend or family member helping you reload under duress It could be possible to mix up the rounds when reloading. I clearly mark my upper on the side in white oil ink (300AAC only) and I purchased some 300 AAC take down pins which rock. http://www.amazon.com/gp/product/B00PZCOMAC/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1
    They make black rubber bands for magazines which indicate 300AAC
    Of course you cannot depend completely on the bands, if one pops off you don’t want to accidentally jam it into your.223.
    The fact is that If you own both calibers the danger is always there. As a prepper you really need both size guns in my opinion. 300AAC has many advantages over its tiny 22 cousin. In vietnam it was shown that .223 rounds would typically be deflected by jungle growth and miss target, while the 7.62x 39 bullets of the Vietcong would stay truer through the foliage and land home. The Government toyed with the idea of transitioning but in the end is was not cost effective. I dont have the cost/kill restrictions that the gvnmt does. I want a primary weapons system which is light weight and hits hard. If the enemy and I are slinging lead at each other, I want my lead bigger. That being said, if doomsday hits I only have so many thousand rounds of 300AAC. When I run out, Im going to need something to shoot. .223 is readily available and perfectly acceptable in a pinch so I have a 5.56/.223 and many many rounds. My philosophy of use is this, I don’t want to be shot by a tango that I just shot. I want a hard hitting man stopper. But in a pinch .223 is better than a rock.

    • Shoot Straight says

      I just built a 300 Blackout and after reading all the articles as to what could possibly happen, I made a decision to keep my AR15 223/5.56 as a black rifle. I built the 300 Blackout in Dark earth. I also only us Dark Earth magazines in my 300 and black magazines in my 5.56. I guess you could still make a mistake, but it at least is a potential problem solver.

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