Has anyone shot 5.56 ammo out of their R15, or do you have any information on if it should be shot out of it? I've seen quite a bit of conflicting data on this, and was curious if anyone had any experience.

is the barrel stamped 5.56?

if you dont see anything on the gun just call remington and im sure they will know

It's not stamped with 5.56, but I saw on another forum an email reply back to an R15 owner from Bushmaster's engineering and they said it was made with the wylde chamber and could handle both.

Is there any easy way to tell how it's chambered?

It should be stamped on te lower receiver. If it says 5.56 it will take both. If it says .223 only use .223 ammo

On AR-15.com it was determined in a lengthy thread that they do have the hybrid chamber. I will try to find that thread when I get a chance.

Found the post from Bushmaster that I refered to before.

Hello,

Subject: Chambers

The barrels have a custom match hybrid chambering that uses the tighter .223 SAAMI Spec headspace from the shoulder of the chamber to the bolt face. It has the longer “Leade” or throat that will accommodate the 5.56mm ammunition so it can be used without developing higher pressures as in a .223 caliber chamber that have a shorter “Leade” or throat.
Both 5.56mm and .223 caliber ammunition can safely be used in the rifles.

The 1:9 twist barrels will stabilize bullets from 40 to 75 grains.

Thank you,

Jim Eden
Technical Support
Bushmaster Firearms International, LLC
Office: 1-800-883-6229 ext. 277
Fax: 207-892-8068

I haven't shot any 5.56 ammo out of mine yet, but have a bunch of it and was just wanting to see if anyone had already done it and had experience before I tried.