View Full Version : What caliber uppers fit the AR-15?

November 4, 2009, 11:28 PM
What caliber uppers fit the AR-15? I know the .308 does not fit however the 6.8 and 5.7x28 do. What other calibers upper fit the AR-15 lowers?

November 4, 2009, 11:52 PM
By this question, I think you're asking what calibers can be fired in upper receivers that can fit an AR15 lower.

I think this will answer your question...


Enjoy! :D:D

November 5, 2009, 12:31 AM
204 ruger
6.5 grendel

these are the ones that come to my mind. im sure others will add more

November 5, 2009, 12:32 AM
add the 308

November 5, 2009, 12:48 AM
no a 308 upper will NOT fit an AR-15 lower. that is an AR-10. much larger mag well

November 5, 2009, 07:47 AM
I'm glad Alaskaman pointed that out. The AR-10 is a different sized lower built to handle the .308 length case and variations can be had in any factory produced cartridge that uses .308 as the parent (7mm-08, .260, etc).

What you need to do is search threads. Members of this forum discussed this topic a few times and there is 1 thread with a comprehensive list of all available AR-15 calibers listed for your viewing pleasure.

November 5, 2009, 08:06 AM
The 300 whisper/ 300-221 uses a .308 caliber bullet.

November 5, 2009, 08:47 AM
Just join the NRA and read this months copy of American Rifleman when they send it to you in the mail.

November 5, 2009, 09:19 AM
Thanks to all for the info. I am an NRA member and this list helps.

November 5, 2009, 09:39 AM
Here in Indiana there is a booming business in necking up the 25wssm to all kinds of large caliber rounds with different names. When the DNR legalized deer hunting with rifles firing pistol cartridges, it spawned a whole slew of wildcatting. As long as the cartridge length is between 1.16 and 1.625 and fires a bullet .357 or larger it is legal. The 25wssm works as a great starting point for this, and you can hardly imagine the cool cartridges they have come out with!

I know it doesn't answer the OP's question, but come on, its cool!

November 5, 2009, 10:45 AM
Thanks to all for the info. I am an NRA member and this list helps.

Do you get the American Rifleman Magazine with your membership? There is a good article that talks about this exact topic in there this past month.

March 5, 2011, 11:40 PM
alaskaman94 243 upper will not fit ar 15 lower it's to long needs to be an ar 10 just to let you know

March 5, 2011, 11:49 PM
Welcome to the site! :D

March 6, 2011, 04:39 AM
Jellybean, the normal .243 Winchester won't fit the AR15 lower, but the .243 WSSM will.

March 6, 2011, 12:31 PM
How about the new .30 RAR? Just out in the latest Book of the AR-15, the .30 RAR will revolutionize the AR and make it what it should be! :rolleyes:

Uses a .308 bolt face, tho. And the bolt carrier, I've read it has to use a different upper, too.

Can it drop on an AR15 lower or not? The overall length was restricted to use the AR15 mag well.

What's funny is Rem owns AAC, who's marketing the .300 BLK as a Whisper substitute, AND the .30 RAR, and was instrumental in getting the 6.8 to market.

Looks like they had there bases covered 5 years ago, but that's me. Of the three, so far, the 6.8 has been a game changer, and is available from a large number of different sources.

Might be the point, the don't have an exclusive on it - which didn't seem to help the 6.5G any. As for interchangeabilty, the .300 BLK only uses a different barrel, and I can see that as a big item in it's future popularity. It very well may rapidly move up in sales over the next 5 years. But, there won't be cheap milsurp ammo for it ever.

Sasquatch in MN
March 6, 2011, 05:53 PM
Another caliber that works in the AR15 lower is 9mm para.

ohen cepel
March 6, 2011, 06:12 PM
5.45-39 also.