AR .223 to 300 BO ?

[clearcut]

So what's involved to put a 300 BO on a .223 AR platform?can you just change the barrel ? check chamber ?Mags? What do I need to know?
Thanks CC

 

[Panzerschwein]

Change the barrel.

That's it.

 

[clearcut]

no adjustments?
CC

 

[jmorris]

Get another upper, two pins to swap them out, and you are good to go.

 

[Panzerschwein]

no adjustments?
CC

I don't think so.

.300 BLK has the same rim dimensions as .223, so you can use the same bolt head. The cases are more or less the same, save the .300 BLK has the case neck blown out to accept the larger bullet. You can even use the same magazines, as both cartridges have about the same OAL and like I said the dimensions are very similar. This is one of the reasons why .300 BLK, super easy to convert a gun over and you get more or less 7.62x39mm/.30-30 Winchester ballistics from your AR-15.

You might want to buy a basic .300 BLK lower though instead of just the barrel, that way you can easily swap back and forth as you want.

 

[Theohazard]

no adjustments?

You might need to change your buffer weight, but not necessarily. And the same could be said for any barrel swap, even between two different 5.56 barrels.

 

[USAF_Vet]

I'd just check headspace if you're using a used bolt. May not be an issue, but never hurts when swapping barrels.

Swapping barrels is the cheapest way to go. Having a dedicated .300 upper is probably the best.

 

[jmorris]

It will be somewhat less than 30-30 ballistics and a bit more than a 357 out of a carbine.

 

[Ranger Roberts]

When I only had one lower I bought a 2nd upper rather than switching barrels, I found it way easier than switching barrels. 2 pins and you are off and running.
**Just a hint** I use different color magazines for 223 and 300blk. Running a 300blk thru your 223 barrel would make for a very bad/painful/expensive day!

 

[MachIVshooter]

I'd just check headspace if you're using a used bolt. May not be an issue, but never hurts when swapping barrels.

This. Personally, I'd by a new bolt if your old one has seen more than a couple hundred rounds. ARs are unique in that in-spec parts produce in-spec headspace, but bolts and receiver extensions do wear together, so you could end up with a headspace issue if you run a used bolt in a new barrel or vice-versa - and it probably wouldn't be evident right away.

 

[eldon519]

Ranger Roberts made a good point. In theory a .300BO will not chamber in a 5.56 gun, but if it experiences extreme bullet setback it can, and it'll blow up the gun if it happens.

 

[Ed Ames]

Ranger Roberts made a good point. In theory a .300BO will not chamber in a 5.56 gun, but if it experiences extreme bullet setback it can, and it'll blow up the gun if it happens.

Wait wait wha?

I thought the point of the vestigial shoulder on the .300 was to make the case diameter at that point (roughly 1.07" from the base) larger than the 5.56x45mm case so it would hang up on the 5.56 chamber? At the same time, the overall length and shape of 5.56 would cause it to hang up in a .300 chamber? Was I giving too much credit?

You are probably 100% correct, but it seems like they came so close to preventing that problem so I wish you were wrong.

 

[Theohazard]

I've seen several well-documented accounts of 300 BO rounds chambering in a 5.56 chamber. When the bullet hits the smaller 5.56 throat, it pushes back into the case and the bolt closes. Then when the rifle is fired a kaboom happens.

Though I wonder how many of those happened because of badly-crimped reloads or improper use of the forward assist. Or some combination of both.

 

[eldon519]

I've never thought about improper use of forward assist but now that you mentioned it, I could see a stubborn soul blowing up their rifle that way.

Ed, I don't have a .300 round for comparison and have only seen reports with pictures on the interwebs, but I believe it is only the bullet and not the brass that prevents the chambering. Could be mistaken though.

 

[Theohazard]

I don't have a .300 round for comparison and have only seen reports with pictures on the interwebs, but I believe it is only the bullet and not the brass that prevents the chambering. Could be mistaken though.

That's correct. If the bullet sets back into the case, it can chamber.

 

[Ed Ames]

Eldon, Theo, thanks for the correction!

It is a shame they couldn't work something out with the taper or a longer neck to remove the cross contamination possibility, considering how many people will share mags. I think I'm going to go to 20rd mags for .300 and 30rd for 5.56 as a personal policy.

 

[Walkalong]

Change the barrel, maybe change the buffer, and you still have one gun, just a different caliber. Buy an upper and you have two guns.

I went the first route, but then bought a better .223 upper to replace the one I had before.

 

[dogmush]

Another vote for different color mags. I use FDE for my .300, and black for 5.56.

I have a dedicated .300 lower, that is also FDE so it's an easy visual. Mags have to match the lower.

Also, fwiw, I tried it with a .300 reload (sans powder) and got it to chamber in my 5.56. Dropped the bolt with the release, and moderate tap on the FA pushed a crimped .300 into the case. Something to watch for anyway.

 

[68wj]

Eldon, Theo, thanks for the correction!

It is a shame they couldn't work something out with the taper or a longer neck to remove the cross contamination possibility, considering how many people will share mags. I think I'm going to go to 20rd mags for .300 and 30rd for 5.56 as a personal policy.

The 7.62x40 WT has a longer case for a 30cal option. You could also look at the 277 Wolverine if you want to use a 5.56 mag and bolt, and get better supersonic performance with still good subsonic.

If you are doing the seperate upper and mags option anyway, consider something like a 6.8 SPC for even more power.

 

[Ed Ames]

Grr...my wallet was probably better off with me not knowing about .277 wolverine.

 

[crazysccrmd]

Grr...my wallet was probably better off with me not knowing about .277 wolverine.

Check out maddogweapons.com, he's got some sales going on barrels right now. It's a pretty awesome little cartridge.

 

[Ibmikey]

A second complete upper or rifle is more desired. If you use your current BCG with any new barrel you should change the bolt to a new one as the bolt will wear to the lock up of the original barrel and may be off in headspace if swapped around. Several companies make rubber bands to mark magazines for 300 Blackout, i mark my rifles as well since a normal shooting outing for me includes a half dozen and more AR's of various calibers, along with my other range toys.

 

[jmorris]

Grr...my wallet was probably better off with me not knowing about .277 wolverine.

I think I will try the 6.5 Grendel next, the 300 doesn't really do anything for me but you can't have one of everything without one.

 

[DougW]

6.8SPC takes a barrel and a bolt change, along with dedicated 6.8 magazines. Converted one of my carbines to compare to my friends .300. I am very happy with the 6.8SPC.

 

[68wj]

I think I will try the 6.5 Grendel next, the 300 doesn't really do anything for me but you can't have one of everything without one.

For something with ammo on the shelf, I would do this too were it not for the 6.8. Both are very good cartridges. Even if I asked mother-may-I to the government for a suppressor, I have no use for subsonic and would prefer either one in supersonic/suppressed format over the BO.