Colossal AR Failure: Shooting 300 Blackout In A Gun Chambered For 5.56mm

BY Herschel Smith
1 month ago

Ken, WiscoDave and I were just discussing this a few days ago.  If you have both of these guns, make sure you have your 300 BO magazines marked, taped or otherwise indicated so that your gun doesn’t blow up in your face.


Comments

  1. On May 18, 2021 at 1:22 am, James said:

    The gas pressure level to the receiver via the gas block has no bearing on a receiver/bolt/carrier failure. This is a subpar part/specification failure if using SAAMI spec ammo. Or a barrel obstruction.

    Stone designed pressure failure to blow out the bolt/carrier through the bottom of the carrier out of the magwell. It worked perfectly here.

    One of my 3gun bros blew up his 300blk by erroneously handloading a double powder charge on a subsonic 220gr load. It looked exactly like that; don’t do that.

  2. On May 18, 2021 at 6:34 am, Ken said:

    I have a wide tan stripe painted across the bottom of my 300 Blackout mags but I also make sure that magazines for the 300 are not even in the same room as a 5.56 rifle and vice versa. I also don’t take both calibers to the range at the same time.

  3. On May 18, 2021 at 7:42 am, James said:

    I will say definitely have different mags,for ease they make them clearly marked .300 now for folks who own rifles that are otherwise similar excepting cartridge.I agree with other James,don’t overload on any round!

  4. On May 18, 2021 at 7:53 am, ragman said:

    Never did this one but I’m guilty of loading a.40 into a.45 ACP. Didn’t work out too well.

  5. On May 18, 2021 at 8:45 am, Ned said:

    I use different color mags (FDE) and a different brand of mags in 300 BO. And like Ken, I don’t take both calibers to the range at the same time.

    As an RSO, I’ve found brass at the range where someone fired 300 Win Mag in a 300 Weatherby Mag.

    If it will fit and fire, it can happen.

  6. On May 18, 2021 at 1:26 pm, Matt said:

    When I load up a magazine I put a piece of masking tape on the mag identifying the caliber, grain and manufacturer of the ammo. People think it’s a bit over the top, but it does prevent caliber mix-up. And if there is an ammo issue, I know who is the manufacturer.

  7. On May 18, 2021 at 2:21 pm, Okanogan Offgrid said:

    I use Magpul polymer mags for 5.56 and metal mags for .300 Blackout. Not just a different appearance, but a different feel.

  8. On May 18, 2021 at 5:27 pm, Frank Clarke said:

    I’m thunderstruck that it would even fit in the chamber…

  9. On May 18, 2021 at 7:17 pm, Chad C. Mulligan said:

    Why do people who do these videos feel it’s necessary to talk-talk-talk with the camera on them. Do they have an ego problem?

  10. On May 18, 2021 at 10:16 pm, Georgiaboy61 said:

    It is vital to label or otherwise unambiguously identify not just magazines loaded with 300 Blackout cartridges, but AR15s chambered to fire it. Word to the wise: There are manufacturers out there making uppers which are chambered for the round, but are not clearly-marked as such, or are marked in such a way as have the information obscured by after-market accessories, fore-end rails, etc.

    It is also germane to note – especially for the newer/less-experienced shooters – that just because a lower is marked “multi-caliber” or “5.56×45/.223” does not automatically mean that the upper is in the same caliber! Any run-of-the-mill 5.56/.223 upper can be converted to 300BO simply by swapping uppers.

    Cardinal rule of safety: Do not load into any firearm ammunition of which whose identifying characteristics (caliber, specific cartridge, etc.) you are uncertain. Moreover, if you are at all uncertain what a particular firearm or upper shoots, do not use it until it can be examined by a qualified gunsmith, including a chamber cast if necessary.

    Ancillary to that, be cautious with used firearms of all kinds, paying particular attention to the possibility the FA was modified, rebarreled in another caliber, or the like.

    Military surplus antique/C&R (curio and relic) FAs are lots of fun and fascinating to collect, but those cautions apply as well, with the additional ones to pay attention to the age of the steel and the particular characteristics of the ammunition appropriate for it. Again, if in doubt that a given collectable is safe to fire, have a qualified gunsmith examined the firearm.

    A case in point would be the Swedish Mauser, chambered in excellent long-action 6.5×55. When designing the ammunition, care was taken to make its case head wider than the 7×57 Mauser which had already been manufactured, and to make the 6.5×55 slightly longer, to prevent it from being mischambered in a Mauser designed for 7×57. Reloading manuals down-grade loads for the Swedish Mauser by about 25% below the real potential of the cartridge due to concerns about modern, high-pressure hunting loads being fired in vintage rifles. Sure enough, if you examine the historical record, they’re duplicating the power/pressure of those older cartridges.

  11. On May 18, 2021 at 10:17 pm, Georgiaboy61 said:

    Re: “Any run-of-the-mill 5.56/.223 upper can be converted to 300BO simply by swapping uppers. ”

    Should have said “run of the mill 5.56/.223 rifle or carbine…” … my apologies for the error.

  12. On May 19, 2021 at 3:47 pm, Bill Sullivan said:

    Frank Clarke- I understand that if a .300 Blackout gets pushed into the chamber, the .30 caliber bullet gets stuffed back into the powder charge. The end result is an attempt to force the bullet down a .22 caliber bore, with the same result as a blocked bore. Possibly assisted by a compressed powder charge. Not good, either way.

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You are currently reading "Colossal AR Failure: Shooting 300 Blackout In A Gun Chambered For 5.56mm", entry #27456 on The Captain's Journal.

This article is filed under the category(s) Firearms,Guns and was published May 17th, 2021 by Herschel Smith.

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