Wrong ammo for wrong rifle

AR/M4 Beyond 5.56/.223
1

I caught myself making a major boo-boo yesterday at the range that could have ended poorly.
I’m relating this story here so that no one else makes the mistake that I made and avoids any potential injury or worse.
I took both my AR15 and my 300 Blackout to the range to poke some holes in paper and zero my sights.
I keep my 300blk ammo in my black windowed Pmags with white lettering that says 300BLK on both sides.
The purpose is to avoid accidentally loading the wrong ammo into the wrong rifle.
The plan was a good one but unfortunately I deviated for my own SOP and loaded some 300 supers in a standard (unmarked) USGI mag.
At one point I had several mags of varying types on the bench and I loaded a mag into my AR15 that is setup for 5.56, when I released the bolt it didn’t sound quite right.
Instead of firing the rifle I decided to look and see if the bolt had seated correctly and what I found was that it wasn’t completely forward, there seemed to be a small gap.
Instead of hitting the forward assist I pulled the bolt back and magazine out only to discover that I had just partially loaded a 300blk into a 5.56 chamber.
I’m pretty sure that if I would have pulled the trigger the round would have gone off but it would not have travelled down the barrel because of it’s larger diameter, that would not have ended very well.
I was extremely upset with myself but in the long run I was glad that when something didn’t sound right I took the extra moment to check and see why.

LESSON LEARNED: Keep my ammo separated and properly marked and keep my rifles separated as well with a visual check of which ammo is to be loaded into which rifle.

2


You wouldn’t have been the first. Thank goodness you weren’t the second (or third or any number at all)

J’ever wonder how fast the twist rate would have to be to stabilize a bullet that long?

3

Sounds like good situational awareness saved the day.

Thanks for sharing.

4

Good for you. You screwed up, but prevented a mishap that you have now learned to prevent.

I never have loaded 5.56mm mags and 300BLK mags side-by-side. Ever. I load 300BLK in a magazine, and the magazine goes in the rifle immediately for exactly this reason.

5

A couple of trips ago to the range I fired 6 or so 5.56 rounds through my 300BLK upper before realizing it.

6

This is sound advice. I started another thread about a friend who made a similar mistake. He fired two rounds of .223 through his 6.8 mm upper and the brass was really beat up. I was surprised that the cases did not rupture. He is lucky he did not wind up with gas burns on his face.

7

I use Hex-Mags as my only .300 BLK magazine while I use Magpul, Lancer, HK polymer and USGI for my 5.56. This works well for me thus far.

Glad to hear you had a questioning attitude when something didn’t sound right…saved you some pain.

8

Magpul 30rd in FDE for my 5.56, and in Black for the Blackout. I am the only one who loads my mags, and I’m darn sure there are no distractions while I’m doing it.
To the OP…be glad your bullet was seated or crimped tight enough that it didn’t set back into the case when the BCG rammed the tip of the bullet into the chamber. Had the bolt completely closed in a situation like that, you could have had a lot worse of a day.

9

If a slight gap could be visually identified, the firing pin would not reach the primer. Had you smashed the FA for a bit, you might have achieved locking, which would have ended poorly.

From Tapatalk:
Jack Leuba
Knight’s Armament Company: Military/Govt Product Liaison
F2S Consulting: Director of Shooting Stuff

10

I released the bolt it didn’t sound quite right.

Stopping to see why it didn’t sound right has saved many a finger, hand and maybe a few lives.

If it does sound right, feel right, takes more force that normal, stop and see why . . .

11

I am going to have to try and stuff a 300 BO round into a 5.56 barrel. I wasn’t aware it being possible.

12

Guys have done it, IG and blew up their rifle. The length of the 300 from base to shoulder is short enough to allow the round to fit ina 5.56 chamber

13

Thanks. This cut-away is a fantastic illustration. Drawing (or pushing here) copper jacketed lead wire = not so fantastic.

Thanks too to the OP for sharing the warning.

14

The photo stories about these (and I’ve seen several) usually show up on . . . a different website. I remember RSilvers being asked about this a while back and IIRC his reply was that the specific bullets used or recommended by Remington and AAC had profiles that would not allow seating of the cartridge in a 5.56 chamber - assuming the bullet is tightly crimped and no one smashes the forward-assist. Handloaders and other manufacturers may use other bullets that don’t interfere like this. I would be especially interested if anyone has had one of these kabooms using Freedom Group ammo (Remington, AAC, Barnes).

15

It’s an issue.
There are new .300 Blk loads that are designed to prevent this from happening.
Some kBs have occurred without the abuse of the FA.

16

I found the picture of the .223 brass that was fired in a 6.8spc upper. The shooter and someone standing next to him got hit with a lot of gas.

17

300 is clear… 300 is clear… 300 is clear…

18

That’s the way I do it, all Lancer translucent mags I own are for 300blk. All pmags are for 556 only.

I do not cross them…ever.

Sent from my SAMSUNG-SM-N900A using Tapatalk

19

This is why I have a personal rule of only one type of ammo on the bench at a time. I had several bolt-actions in various calibers, some of which would allow incorrect rounds to chamber with potentially deadly results. Working several years at a gun store with attached pistol and rifle ranges I had more than enough opportunity to see the results of such errors. Fortunately no serious injuries, at least to the shooters. Bulged and ruptured barrels, pressure welded actions, explosive disassembly - expensive safety lessons learned.

20

this is enough of a potential issue to keep me out of 300BO (and for me the caliber doesn’t achieve anything I don’t already have or need). Getting to the point in life that I want to simplify and don’t want to have to wonder which ammo I have in my AR mags. Less drama and less stress is a good thing.