How much you wanna bet this is a one-shot or bolt-action PISTOL that the loon can stuff in a small backpack or whatever and slip away unnoticed?
Like maybe a Remington XP100, Savage Striker (which is actually a two-round mag plus one up the pipe gun) or Thomson Center Contender?
All are available in 223, all have the accuracy to pull this crap off with a decent scope and some crossed sticks for a field brace. The Thomson has an advantage: buy it in some other caliber, then buy a 223 barrel cash'n'carry and no gov't agency would ever know you have a 223 at all.
Heck, you could conceal a Contender IWB, although you'd walk a little bit funny.