Make sure everything is tight. To make sure, I'd take the scope and mounts and bases off and put them back on. Using a little lock tite or finger nail polish as you go. It doesn't take much scope movement to put you off.
Make sure you have proper clearance between the stock and the barrel. Check it cold and then again after you start shooting. Clean the bore good. Very good. Use a bore guide and clean from the receiver end. I doubt your barrel is shot out. It'd take a lot of shooting to shoot out a .223. Even if a fellow is playing Rambo. My guess in that department would be copper build up.
What size target dot are you shooting at? At 50 yards, it shouldn't be bigger than 1/2" if that. Also, how's your bench technique? Have you got a good solid bench? Are you shooting from a good rest or firm bags? Are you capable of bug hole shooting? No disrepect intended.
Try some other brands of ammo. Some rifles like Rem, some like Win, some like Fed. Some rifles can't stand the high dollar stuff and shoot the cheapo stuff like a lazer.
Before you start spending a lot of money on scopes and stocks and such, remember that if you put a $1000.00 saddle on a $100.00 horse, you still got a $100.00 horse. I'd give the rifle a chance to be all it can be before you decide to put a lot of money in it. I don't know what you plan on doing with the rifle but those groups aren't that bad if you plan on using the rifle as a truck gun or a walk-a-round. Tighten them up a little and they wouldn't be bad at all for a factory rifle shooting store bought ammo. To properly exploit any rifle's accuracy, you need to reload. But that's another story.
FYI, in one of the rooms, there's a thread about how to be a better shot. Wouldn't hurt to read over that.
