BudsGunShop.com - 556 or 223

556 Nato 1:8 twist stamped on the barrel.
The 556 barrel can shoot both 556 and 223 no problem, you can see a very slight drop in accuracy when shooting 223 at longer ranges, but its not enough that most shooters with most AR15 applications won't notice.
If your shooting 223 at long range on a regular basis, pinpoint accuracy really matters,and want to still be able to shoot 556, a 223Wylde barrel is the best bet.
But for home defense and inside of 400 yards 556 barrel is perfect. My home defense AR is a Ruger 556 MPR, and I love it.

Mark, yes this Ruger is chambered in 5.56.

The barrel is marked 5.56, you can shoot .223 in a 5.56 barrel, but not the other way around.

It is chambered for 5.56 NATO but will function reliability with both 223 and 556. I hope this helps!