You cannot fire form loaded 223ammo in a 7 TCU barrel. The brass will rupture at the neck/shoulder area and the bullet will not go straight, may even get stuck in the bore. Fire forming requires that the 223 case be necked up to 7mm, loaded with a 7mm bullet (with published load data) and then fired. By the way very nice gun at an awesome price, if you get tired of it let me know.
Be SAFE!
RicMic