300 Blackout in a .223 Wylde AR-15 Kaboom

300 Blackout in a .223 Wylde AR-15 Kaboom

One of the huge draws of the 300 AAC Blackout (AKA 300 BLK) is that it can use the same bolt and magazines as a .223/5.56 AR-15. The only downside? It can use the same bolt and magazines as the .223/5.56 AR-15. A friend and reader presented me with a box of AR-15 upper receiver parts this past weekend that vividly illustrates what happens when a distracted or negligent person loads magazines. A single 300 BLK cartridge somehow found it's way into a box of loose .223 cartridges, and was subsequently loaded into a 30-round PMAG, which was then handed to an AR-15 shooter shooting a rifle chambered in .223 Wylde (a chambering that is supposed to shoot both .223 Remington and 5.56 NATO equally well). The .223 cartridges in the magazine went "bang-bang-bang." The 300 Blackout round apparently fed into the chamber just fine, the shooter pulled the trigger, and what you'll see on the following pages were the result of the ensuing kaboom. Luckily, the shooter was shaken, but uninjured. photo 1 This is the remains of the upper receiver, as I've been able to partially reassemble it. You'll note that the part below the ejection port has been destroyed. The front matter (barrel, gas tube, handguard, etc) with the cartridge and bullet lodged inside, remain with the owner. He is going to attempt to salvage some of the parts, along with the lower, which was also salvageable. The upper receiver, charging handle, and bolt carrier group are a total loss. You'll note that I was able to get the bolt back into the upper receiver for the photo, but that there are parts missing. Some were destroyed during the kaboom, and some during the process of prying things apart. photo 3 When they were able to pry the bolt carrier group out of the upper and remove the bolt, the cartridge case head came with it, while the rest of the cartridge case and the bullet remained lodged in the barrel. photo 2 photo 1 This split/fractured bolt carrier seems to have absorbed the bulk of the internal damage, and both it and the bolt are now scrap. photo 5 The rear of the upper was also split, but I don't know if this was from the kaboom or the salvage process. photo 4 As a matter of simply physics, explosions follow the path of least resistance, which in the AR-15, is typically down the magwell. This is reflected in the condition of the 30-round PMAG that was blown out of the rifle. photo 3 photo 2 Here's my big question: is it normal for a 300 BLK cartridge to chamber well enough for the bolt to close under normal conditions in a 5.56 NATO or .223 Remington chambered AR-15 rifle, or is perhaps possible that the rifle fired without the bolt fully closing? I'm sure there are readers out there far better equipped to answer this question than I am.

116 thoughts on “300 Blackout in a .223 Wylde AR-15 Kaboom

  1. since the neck of the 223 can be cutoff and resized to reloaded to 300blk it is shorter than a 223 and probably slam fired while never chambering

  2. How in the hell can you mistake a 300AAC and a 223 loading a magazine? Just the size of the 30 cal. 115+ grain bullet is twice to four times the size of a 223. I have both and believe me you will know the difference right away.

  3. weak or no crimp so when it was chambered it pushed the tip back in the case and subsequently closed enough to fire.

  4. Simple math people, slamming a 30 caliber bullet into a 22 caliber chamber should not even happen…I think it went off without even having fully chambered, which tells me someone built something wrong.

  5. BULL SHIT A .300 IN DIAMETER ROUND WILL NOT CHAMBER IN A .223 IN DIAMETER BARREL AND ALLOW THE BOLT TO LOCK, UNLESS THE HEADSPACE WAS WAY THE HELL OFF.

  6. It's easy if you get in a hurry. There's only one infallible person on earth – apparently that's you.

  7. Wrong. Different. Better for some missions and situations. Heavier, worse trigger, not nearly as ergo, and not as customizable / accessorizable.

  8. Possible but the rifle wasn't really That worn and most parts seem like they are quite new , I believe it is more that the cartridge does fully load and lock the bolt carrier group into place

  9. If the 300 blk bullet is not properly crimped it will push back into the casing allowing it to chamber, lock and fire..

  10. If it was a standard bolt and bolt carrier group design, the firing pin will not protrude out of the bolt face until the bolt carrier is fully forward and the bolt has rotated & locked with the barrel lugs. That does not sound like a slam fire, it sound like the momentum of the bolt and bolt carrier group was enough to drive the bullet back into the case enough that the bolt was able to fully seat. It wouldn't really chamber the bullet as much as just poke the nose into the chamber and stick half way in then crush the cartridge size down by driving the bullet back into the case – sounds ugly.
    Can't know for sure if that is how it would work and I am not about to get a 300AAC round anywhere near my 5.56 upper to test out that idea.

  11. 5.56x45mm is the AR chamber….. 7.62x35mm is .300blkout. The nose of the round will go into the chamber and lock. My Daniel Defense barrel just did it.

  12. I believe that 300 BLK may need to be refined so that it may only be shot from specified components ,more robust components. From the Data and testing I have done this is a phenomenal mid range round not alot of energy wasted and all is dumped into Subject/Target,Great for LEO engagements as its documented distance is beyond Most any LEO

  13. If you are the fallible one to get in a hurry and do this I do not want to be anywhere near you or anybody like you at the range. Firearms are not toys to get in a "hurry" with, that is why people get hurt.

  14. Simple answer, the 223 or 5.56 round headspaces on the shoulder. The shoulder is completely different between these two round. The overall length of the 300 AAC is such that it will fully insert in the chamber of a 5.56 upper. When fired the bullet jams in the barrel (7.62 > 5.56) leaving no other place for the energy to go except out through the path of least resistance.

  15. The 300 BO case neck is closer towards the case head. The 300 BO cases are actually shorter. So only the tip of the 30 cal bullet needs to be able to squeeze into the neck/shoulder of the chamber. The whole 30 cal bullet obviously won't fit into 223/5.56 throat for it to chamber.

  16. Daniel Stoner You never hurry with a firearm. Hurrying creates accidents like this. And as he pointed out, with training you can recognize case differences by eye and feel–which means either the person that loaded this or the person firing just weren't paying attention.

  17. Have to agree with Michael on this one. ALWAYS check your ammo before you put it in a magazine. This seems like a rookie mistake to me or straight up negligence. Every round has it's "size" on the bottom or back of the casing.

  18. 300 BO cases are shorter and their shoulder/necks are set further back than stanard 5.56. So a small 30 cal 300 BO should fit into a 5.56 since the actual 30 cal bullet sits further back towards the case head. Only the tip needs to squeeze past the shoulder/neck of the chamber of the 5.56

  19. Joshua, the stamp on the casing won't help in this case. 5.56 cases can be cut down and used for 300BLK, you have to be alert and look at the bullet size 30 cal vs 22 cal. You can tell the difference by the size of the .308 bullet 115 to 220 grain vs a common 55 – 62 grain 5.56.

  20. How could it have been fully chambered and the bolt locked and fire? There is no way that a .300 "Anthing" can go into a .223 chaber of the same lenght. No amount of wear can account for this happening.

  21. It will chamber enough for the firing pin to be hit by the hammer and blow up your gun. I have seen several blown so far. I use only 20 round mags for my 300 and 30 round mags for my .223.

  22. The bullet would have had to be seated very deep to let the head space be close enough for it to be fired. Glad no one was injured.

  23. I am not an expert armorer but I doubt that a well maintained weapon like that would fire without the chamber locked. I think the bullet firmly lodged in the barrel is telling you everything you need to know about what happened.

  24. A .30 cal will not fit in a .223 chamber, no matter what you do. The neck of the case will never get close to chambering since it's .308"-.224"= .084" larger. Therefore, I say it might have been something else, but not a chambered .300 BLK round.

  25. Likely the bullet was not crimped properly and was pushed back into the airspace in the brass. Either way this is not a single mistake, but a chain of mistakes, any of which not made could have prevented this.

  26. I've tried out of curiosity and 300 BLK won't chamber in any of my 5.56mm uppers. The theory that there was no crimp and the bullet was pushed back does make a bit of sense if the round was hand reloaded.

  27. Daniel Stoner
    I will agree here that getting in a hurry with rifle loads is mistake #1, That round should not load fully into that chamber, and would set back too far , obviously it must have fired , so there are a series of mistakes here. That would have been a scary blowout.

  28. I believe the force of the bolt going into battery pushed the .30cal bullet into the case allowing the bolt to completely close into battery.

  29. I believe the force of the bolt going into battery pushed the .30cal bullet into the case allowing the bolt to completely close into battery.

  30. seen something almost like this happen @ deer camp last week, hunting partner who brought his .270 and his 300 WM was complanig about a bullet for his win mag not staying in the clip, after I took a look, I noticed because my buddy is older and a bit blind, mixed up his .270 and 300 mag ammo, just one bullet, but sometimes shit happens.. We're all glad the clip would'nt hold it

  31. The round could not have ever fully chambered, its a simple issue of size, the round would have fit the mag, and probably gone into the weapon just fine, however the shooter should have noted a difference when it went in, or whoever was loading the weapons magazine should have noted a difference in the round.

  32. 6.8 SPC FTW!!!!
    Remember how the 6.8 got a bad rap for needing a new bolt and barrel.
    Doesn't look so bad now does it.
    Yea I'm a fan boy,
    But this is exactly why I won't own one.
    I admit I'm a moron and I absolutely see my self doing this. I personally chose not to be lazy and would rather be certain I will avoid this. All it takes is one small distraction and look at the results.
    All kidding aside, please be careful. This is not something we need In the news. God forbid the ATF and govt find out, out of concern for our safety they will require a freaking 6 week background check for 300acc bullets and barrels.

  33. This is a result of not loading the blackout long enough, and not crimping it well. Gotta make your ammo properly.

  34. This is a result of not loading the blackout long enough, and not crimping it well. Gotta make your ammo properly.

  35. I read an article years back of shooting a 30-06 through a chamber converted 6.5 Arisaka barrel. The only real effect appeared to be tremendous recoil. The gunsmith thought it was a 7.7mm Arisaka. The NRA tested the rifle and found it appeared to shoot without difficulty other than really rough recoil.

  36. Freakin' scary man,I cringe when I see things like this,glad everybody's o,k,the weapons replaceable,human life,not so much!

  37. no way it fired with the bolt not closed. the bolt and carrier would have came straight back into his shoulder if that were the case. The locking lugs on the carrier saved his life. That carrier just got hit with over 50000 psi of pressure.

  38. there is only really one way I know of this could happen just one disclaimer I do not know the oal of a 300 but I do know it is a 223 size cartridge. Unless the gun malfunctioned and fired with an unlocked bolt maybe the round was not crimped and the force of the bolt shoving it into the chamber caused it to move back further in the case and allowed the bot to fully close. never the less if you have calber's like this you should always check to make sure you are using the right ammo

  39. Search .300 blackout on Wikipedia and there's a swell picture there with a 5.56 NATO round among various .300 Blackout cartridges and you can plainly see how one could easily chamber in a 5.56.

  40. Billy Wardlaw You're probably right about the bullet being pushed back into the casing. I do not know if it would have to be improperly crimped for that to occur. But I am in complete agreement with you. every accident is caused by a chain of mistakes.

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  42. how did he know it was a .300 round? does he have a .300 rifle? If he reload his own ammo I can see where one might get dropped and mixed up.
    When I load a clip full of ammo into a mag I tend to pay attention.
    Was rifle on auto? even then I dont think a spring would have enough force to jamb a .300 object into a .223 hole…
    Is it possible this happened if he crimped a .223 bullet into a .300 casing?

  43. I heard of people putting .40 cal into a 9mm guess what happened ? It happened at Bass pro range a few years back. Does that mean you may put .45 into your 40 cal?
    This is a "bad" article about a good cal. Rifle. I'm betting it happens to pistols more than the 300BLK-.223 rifles.

  44. Answer Yes If the 223 5.56 is resized and cut down to accomidate a 30 cal than once it is locked into that bolt it will explode !! all i have to say is the Lord was with you when you pulled that triger !!

  45. While I'm at it. I was at Academy just this past weekend and customer asked the guy at the gun counter for some .30 cal ammo.
    Gun guy ask what kind?
    Customer said it don't matter
    Gun guy said yes it does what kind of rifle you using?
    Customer says " I don't know" just give me any .30 caliber.
    GHun guy proceeds to explain that there are several different .30 cal style bullets and the customer said really?!

  46. So again. This article is useless like Obama. It can happen with ANY weapon. Some A$$hole just wanted to pick on a 300 BLK for some reason.

  47. As a fromer USMC 2111 I have seen 5.56 ammo were the bullet was set back do to a mis feed round slaming into the side of the barrel extension rather then feed into the chamber. So even a properly Crimped bullet can and will be set back into the case if met with a solid object i.e. the throat or neck area of a .223/5.56 chamber. So now you have a .308 dia. bullet sitting over a compressed load of fast burning powder. forcing that down a .224 bore is bad news, as the pictures show. FWIW bullets like the Seirra match king 125 gr. don't have a cannelure further redusing the effect of a crimp.

  48. That or it was using a very soft primer, like a federal (they are more touchy) and the FP had enough forward momentum to set it off. Slam fires do happen.

  49. Not quite.. teh .308's are long enough to make up the difference and the ogive of the bullet should catch on the throat before fully chambered.. should.

  50. slam fire.. cycle some rounds through your chamber and let the bolt fully slam home.. even hard primers will quite frequently show a light dimple where the FP hit the primer.. with a soft primer.. detonation is feasible

    I'd bet on bullet set back though..

  51. As stated by many commenters,the ONLY way this .300 round could have been inserted into an AR-15 is IF (im pretty sure) the bullet,was pushed back into the case,crushing the powder,then the bolt COULD have closed all the way,with the bolt locking lugs,actually locked,then the rifle was fired,,,with the oversize round fired,the bullet could NOT be expelled thru the barrel,the 50000 PSI had to go somewhere,thru the point of least resistance.

  52. first of all things! never let someone else load your mags for you. the one firing the weapon should be the one to handle the ammo . in my opinion if you cant do it your self you should not fire the weapon . second the rounds are different sizes regardless of how close they look . the 300 blk would not fully chamber into that barrel . third im sure everyone of the people involved are safe shooters . but this seems like a case of complacence on everyones behalf

  53. The firing pin can not go past the face of the bolt unless the bolt is closed. In an over pressure case like these. The bolt is so wedged against the barrel extension it can not turn to unlock but the bolt carrier is forced to the rear. So the bolt carrier is forced to slightly rotate and pops the left side off the upper or cracks the upper open. It may look like the BCG is out of battery but more then likely the BC is to the rear but the bolt is stuck in the locking lugs.

  54. Never seen a slam-fire in an AR15 with ANY type of primer. Likely not caused by a "soft" primer rather than a severely gunked up bolt/carrier keeping the FP forward in the bolt.

    Wouldn't it make more sense to move the shoulder of the cartridge forward (on the .300AAC) rather than just necking up a .223 casing? This is the reason for making the .357 and .44 magnums longer, so that they wouldn't fit in the shorter "special" cylinders. Shouldn't the casing prevent the round from chambering in a .223 chamber rather than just relying on a crimp to prevent it?

  55. customizable only matters to the city cowboy thats trying to play war. Who really needs a flash light on a gun? Just gives your position away, might get hit with a paint ball doin that.

  56. It won't fit and the striker couldn't have hit the pin! the bolt would have to rotate fully into battery lock up before the striker could even be released by the trigger group so something aint right with this story!

  57. It's a story, Period, nothing adds up, the round won't fit, the bolt couldn't rotate into battery so the trigger group couldn't release the striker and even if the primary and secondary engagements hadn't grabbed the striker and it followed the bolt it would have jammed up to far out of battery to allow the striker to hit the firing pin! "But" I have seen a weapon that looked like this one because the nimrod stuffed a bullet halfway down the barrel with an un-charged round then cycled a new one up that was charged before checking why his weapon didn't shoot and cycle on it's own the first time and found out the hard way why he should "not" own a weapon in the first place much less reload his own ammo.

  58. make the 300 BLK longer????? Sort of goes against the whole idea of the design. The better idea is to pay attention to what's going on if you own one. A better example then the .357 and .44 would be the .270 win and the 30-06. Either way the operater needs to be more diligent

  59. I am a reloader and as such I know a little something about bullet diameters. There is no way that I am aware of to force a .308 dia. bullet into a .223 dia. chamber. That is a difference of .085. You might be able to jam that much difference with a good bolt action, but with an AR-15? I must cry foul. I believe Jody haas the correct theory. The 300 BLK went off long before the bolt closed and the weapon was in battery.

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  61. The bullet has to push back into the cartridge in order for the round to chamber. Since factory 300AAC ammo is in limited supply, there are a lot of handloading of ammo going on. The regular crimp dies don't put a hard crimp on the bullet and it can get pushed back. This can happen easier if the bullet has no cannelure. I recently started using a Lee factory crimp type die to help secure the bullet in the cartridge. Even on a 300AAC barrel, soft point or hollow point bullets may catch when feeding and push back if you don't have a good crimp. I have coyote tan furniture on my 300AAC carbine and use tan magazines for 300AAC ammo just to help keep them separate. Pay attention, don't rush and be safe.

  62. Won't work that way, 300 AAC Blackout will not chamber in a 5.56 rifle, and a properly loaded round will not seat deep enough in the chamber to reset the trigger, even in a round where the neck has not been crimped. I'm calling BS either that round was so badly deformed at the neck that the bullet was barely seated and the powder charge was not correct (Lil' Gun, H110, and A1680 almost completely consume the case volume).

  63. Had this just happen to me and been trying everywhere to finded out why!!I had the gas and feed problems w/123gr Hot Core SP and I meticulously went though and cut, trim, shaped reshaped and dry fit in the weapon and calipered up and down and a base gauge dry fit again and I am running on a Spikes Tactical with just a barrel change and cycled perfectly 25 times then KABOOM same result as above and I don't know why but I do know it worked flawlessly as a 5.56, the bolt was a MIL-SPEC Chromed Rock River and I thought my hand was gone and it scared the SH*&T out of me. It BLEW my upper apart, bolt destroyed and the upper was warped something awful along with a barrel split at the feed-ramp..This thing cooked off a round in the open position period..But man when it worked it was more accurate hard hitting and I loved it and I still do but this barrel thing has to be worked out, even inspected my spent rds and they were perfect..maybe something inside the breach lock? But I do know this guy is telling my story!

  64. Had this just happen to me and been trying everywhere to finded out why!!I had the gas and feed problems w/123gr Hot Core SP and I meticulously went though and cut, trim, shaped reshaped and dry fit in the weapon and calipered up and down and a base gauge dry fit again and I am running on a Spikes Tactical with just a barrel change and cycled perfectly 25 times then KABOOM same result as above and I don't know why but I do know it worked flawlessly as a 5.56, the bolt was a MIL-SPEC Chromed Rock River and I thought my hand was gone and it scared the SH*&T out of me. It BLEW my upper apart, bolt destroyed and the upper was warped something awful along with a barrel split at the feed-ramp..This thing cooked off a round in the open position period..But man when it worked it was more accurate hard hitting and I loved it and I still do but this barrel thing has to be worked out, even inspected my spent rds and they were perfect..maybe something inside the breach lock? But I do know this guy is telling my story!

  65. A Titanium firing pin "might" mitigate the issue, somewhat. When the BCG slams to a complete stop… the inertial mass of the firing pin will cause the firing pin to continue its journey forward, denting the cartridge's primer & K@bOOm.

  66. A Titanium firing pin "might" mitigate the issue, somewhat. When the BCG slams to a complete stop… the inertial mass of the firing pin will cause the firing pin to continue its journey forward, denting the cartridge's primer & K@bOOm.

  67. A Titanium firing pin "might" mitigate the issue, somewhat. When the BCG slams to a complete stop… the inertial mass of the firing pin will cause the firing pin to continue its journey forward, denting the cartridge's primer & K@bOOm.

  68. Daniel Stoner well non of that matters, a .30 caliber bullet is not meant to be shot out of a .22 caliber chamber, the fact that it was crimped or not is pale in comparison to the fact that a gun cannot shoot a bullet it isn't mean't to shoot, that would be like loading a 12 gauge with a .20 gauge round, not supposed to do that

  69. Joshua Amis seem like it would be common sense ,, probly maybe explains the large # of kabooms ,, cant be newb reloaders , hey lets blame it on glock ,,, just sipping the koolaid ,,lol

  70. I recently bought a 300BLK AR platform. From the company it was sent with a 223/556 mag in the magazine well. 300blk fits fine in 223/556 mags. The only downside is, instead of the mag holding the casing for a tight fit, they catch the slug, thus giving the rounds a loose fit in the mag. I recently shot the rifle for the first time out of the box, used a MAGPUL PMAG, loaded it to cap, and within 4 shots, had a double feed and a misfire. So, if anyone is shooting 300blk through an AR platform, I suggest finding 300blk mags. Also this is probably WAY off your subject..lol

  71. The .300 Blackout uses 5.56X45mm cases. Cut off at the shoulder and resized to create a .30 cal throat and shoulder. So, the base is a 5.56. For the chamber being a Wylde. It would make no difference if it were a .223, 5.56 Nato or Wylde. As the case diameter are the same and the .300 Blackout case is the same OAL. Nothing in this report says the round actually passed through the barrel. So the action of the bolt carrier going to battery probably did push the bullet in to the casing. As the bullet couldn't travel the barrel. The force followed the least line of resistance and blew back through the action causing a catastrophic failure.

  72. The finish on that rifle speaks to the shooter. Tacticool doesn't always equate to tactical knowledge. Always know what ammo you are loading, its not hard to tell a 300 BLK from a .223 cuz the damn bullet is three times the size. If you rush, and you approach shooting like typing in a google search, your shit blows up. Im sure he learned a valuable lesson, and he is lucky he didn't loose his fingers or his eyesight.

  73. 7.62x35mm was designed to be used in unmodified STANAG mags. To accomplish this with a .30" projectile, the ogive of the .30' bullet is used in place of the shoulder of the 5.56x45mm case to give a proper cartridge column. That being the case, a 7.62×35 round will chamber nearly perfectly every time with the ogive resting on the chamber's shoulder. I agree this design is far from poka-yoke but using the wrong ammo is unequivocally the operator's fault.

  74. It definitely went off without fully chambering. If it had achieved full chamber, the entire front end of the upper would have blown up along with the barrel (the bolt locks in place in the barrel), though the BCG would likely be shredded as well. I would be surprised if enough force could be generated to cause that kind of damage to the magazine, but if it were only mostly closed this would be much more likely.

  75. Alan Dike Federal Primers still have to meet SAAMI specs. I have heard this argument before; however I think there may be a better question. That is is it "soft" enough to be set off by anything less than a solid and intentional primer strike? Having a brand primer that is more responsive to a solid firing pin hit does not necessarily mean that it is more susceptible to being set off by a floating firing pin.

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