On the side on the mag well it is marked "CAL. MULTI"....Does that mean it will accept .223 and .556? Or does it mean something else?

5.56, .223, .300 BO, or whatever caliber that can fit into that mag well.

What’s written on the magwell doesn’t really mean much. What caliber the gun uses at any time depends on what the barrel is chambered for. It’s usually marked on the barrel, and likely says 5.56, which will also shoot .223. If you had a .300 blackout barrel, you could shoot that. Or 9mm, or a number of other calibers with mags that fit in the same magwell.

Just denotes it's a standard generic AR15 lower receiver that is able to be used with any caliber that fits the standard AR15 magwell. There are dozens of calibers able to be used in a standard AR lower.

It's the markings on the upper receiver that dictate which caliber(s) your rifle is chambered in, in that configuration. Look on the side of the barrel. It should state both caliber as well as twist rate. This may be covered by a handguard.

quote:

Originally posted by Dwill104:
What’s written on the magwell doesn’t really mean much. What caliber the gun uses at any time depends on what the barrel is chambered for. It’s usually marked on the barrel, and likely says 5.56, which will also shoot .223. If you had a .300 blackout barrel, you could shoot that. Or 9mm, or a number of other calibers with mags that fit in the same magwell.

5.56 is written on the barrel.