Josh, no Sir. 300Blk is a 30 Caliber Round and 5.56/.223 are 22 Caliber. All you would need my man is a 5.56 Upper to attach to this lower as the lower is universal to both calibers.

DO NOT TRY TO USE 223 OR 5.56 NATO ammo in this gun it is chambered for 300 blackout ammo , also known as 7.62×35mm

Josh, No, this firearm is a 300 blackout firearm not .223/5.56 firearm. Barrel and chamber are much larger for the 7.62 diameter round. 5.56 diameter would be dangerous to fire from that dimension chamber and barrel.

No Josh, this is a 300 Blackout model ..chambered in 300 Blackout, it only functions with 300 Blackout ammunition (AKA 300 AAC) Can't use 223 or 5.56 in this one.