300 Blackout vs 5.56 chamber - Question

I'm posting this question on the M&P 15 thread because I figured I'd get a better response from 'AR' folks then I would if I post it on the 'Lounge', or, elsewhere. Mods, if you feel that this isn't he most appropriate place, please feel free to move it.

Since the 300BO is a .30 cal. projectile and is fitted into a 'necked up' 5.56/.223 casing, and, the same mags and BCG (bolt carrier group) can be used for both the 5.56/.223 & 300 BO, the question that I am going to ask, and, want a general consensus on is this;

'Is it possible for an AR-15, regardless of who manufacturer is, that is chambered for 5.56/.223, both chamber, AND fire, a 300 BO round?'

I'm interested to see what replies I get on this one.

Eric300 said:

I'm posting this question on the M&P 15 thread because I figured I'd get a better response from 'AR' folks then I would if I post it on the 'Lounge', or, elsewhere. Mods, if you feel that this isn't he most appropriate place, please feel free to move it.

Since the 300BO is a .30 cal. projectile and is fitted into a 'necked up' 5.56/.223 casing, and, the same mags and BCG (bolt carrier group) can be used for both the 5.56/.223 & 300 BO, the question that I am going to ask, and, want a general consensus on is this;

'Is it possible for an AR-15, regardless of who manufacturer is, that is chambered for 5.56/.223, both chamber, AND fire, a 300 BO round?'

I'm interested to see what replies I get on this one.

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I presume you are kidding

You want to try a round of .300 BO in a .223 rifle?

You will never push something measuring .30" into a .22" hole


Now the opposite could occur.

A round of .223 could chamber in a 300 BO rifle and fire.

The projectile will just rattle down the barrel and not do much more than that once you set off the primer

Absolutely. Results can be "startling". I never take both calibers to the range at the same time. All my 300 Blackout magazines have 300Blk bands on them and my various 300 Blackout guns have several prominent identifiers on them to indicate 300 Blackout. A loaded 300 Blackout cartridge is short enough that IT WILL chamber in a 223/5.56 chamber and fire if the trigger is pulled.

I have a friend whose brother wasn't paying attention and did just that. AR15=DESTROYED. He was lucky though.

I am not kidding at all.

colt_saa said:

I presume you are kidding

You want to try a round of .300 BO in a .223 rifle?

Of course not. You are interpreting this question wrong. Stand-by and you will see.

You will never push something measuring .30" into a .22" hole

Don't be too sure about that....

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *​

Now the opposite could occur.

A round of .223 could chamber in a 300 BO rifle and fire.

The projectile will just rattle down the barrel and not do much more than that once you set off the primer

Click to expand...

CZU said:

I have a friend whose brother wasn't paying attention and did just that. AR15=DESTROYED. He was lucky though.

Click to expand...

Ahhhhh, now we're getting somewhere.

mckenney99 said:

Absolutely. Results can be "startling". I never take both calibers to the range at the same time. All my 300 Blackout magazines have 300Blk bands on them and my various 300 Blackout guns have several prominent identifiers on them to indicate 300 Blackout. A loaded 300 Blackout cartridge is short enough that IT WILL chamber in a 223/5.56 chamber and fire if the trigger is pulled.

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You are a wise man!

Short answer--yes. But you will not like the results. Don't try it.

colt_saa said:

A round of .223 could chamber in a 300 BO rifle and fire.

The projectile will just rattle down the barrel and not do much more than that once you set off the primer

Click to expand...

But will the bolt close, seeing as the .223/5.56 shoulder length is significantly longer than the .300 BO? Methinks no.

Ok, apparently, this isn't going as I expected. So, before this thread goes sideways, here's what I was getting at......A little while ago, a buddy of mine who is relatively new to AR's, calls me and says that his AR blew up while shooting it. First I asked if he was OK, and other than some minor shrapnel in the face and chest, no serious injuries. Since I knew he had 2 ARs, a 5.56 and a 300BO, I asked him which one. He said it was the 5.56 (no need to mention brand since it's irrelevant to this discussion). He only lives about 5 miles away so I grab my AR 'medical bag' and drive to his house to investigate. After looking at what was left of his AR I start grilling him. Long story short (I know, too late), he had both his 300BO and 5.56 out and was shooting both behind his house. He inadvertently loaded a few rounds of 300BO into his mag and inserted it into his 5.56. The rest is history. I ended up performing a post mortem autopsy on his deceased rifle. The 30 cal bullet made it all the way to the gas port before stopping. I had to hammer it out with a cleaning rod. It extruded to almost 2" long.

The moral of this story is; KNOW what the heck you're doing when handling/shooting firearms!

Enjoy the photos.














Case


Bullet

That is the reason why:

1) All of my 300 AAC magazines are well marked with bands, and
2) I never take 5.56 and 300 AAC to the range at the same time.

All of my .223 magazines are BLACK and all of my 300 BLK magazines are DESERT TAN. In addition I do not take both calibers to the range and the dust cover on the 300 BLK is marked as such in WHITE.

Your friend was very lucky. Thanks for the pictures, it helps to see what damage was done.

I am so paranoid of something like this happening that the rifles cases for my different rifle caliber AR's are different colors. Black cases 223/556, Tan cases 300 Blackout, Green cases 6.8 spc. My Galati International 6 pocket magazine carry pouches are color coded with the calibers/cases. Overkill? Look at the pictures above and reconsider.

Interesting post I've really never tried to chamber a .223 in my .300 BL.
I'll give it a try tomorrow to see if they will chamber....but definitely won't see if they fire…...

andy52 said:

Interesting post I've really never tried to chamber a .223 in my .300 BL.
I'll give it a try tomorrow to see if they will chamber....but definitely won't see if they fire…...

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The danger comes from chambering a 300 AAC in a 5.56/.223 gun. A 5.56/.223 fired in a 300 AAC won't be pretty, but a 300 AAC fired in a 5.56/.223 gun will be disastrous.

Sistema1927 said:

The danger comes from chambering a 300 AAC in a 5.56/.223 gun. A 5.56/.223 fired in a 300 AAC won't be pretty, but a 300 AAC fired in a 5.56/.223 gun will be disastrous.

Click to expand...

What? The damage done in those pics wasn't 'disastrous' enough for you? What's your idea of disastrous?
? lol

I guess the take-away from all of this would be to not load anything that starts with the #3 into a chamber that's starts with the #5. But, those pics are from a 300BO thru a 5.56mm.

rtquig said:

Your friend was very lucky. Thanks for the pictures, it helps to see what damage was done.

Click to expand...

You can never have too many safety reminders!

A 300blk round theoretically should not chamber, but it can get pushed down in cartridge by the BCG enough for the AR firing pin to hit a primer. If you pull the trigger, it may go Kaboom.

The more appropriate question is can a 30 caliber bullet go down a 22 caliber barrel, and the clear answer is NO. Many have tried. None have succeeded.

I put a band of yellow electrical tape around the base of every magazine loaded with 300BLK and NEVER mix .223 and .300 Blk magazines in the same bag. I also do not take both calibers to the range on the same trip.

Don’t know if anybody has ever been killed by loading a blackout round in a .223 rifle, and don’t care to find out either.


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I was on the firing line 4 lanes away with a guy who did exactly that ... fired a .300BO cartridge in a 5.56 barreled rifle.

He was virtually unscathed and I was picking tiny bits of his rifle out of my head and arm for 6 months.