I recently bought a Ruger Bearcat, just for fun. I couldn't shoot it well offhand and after benching it, found out why. It shot around the clock, but none in the center. Another cylinder full duplicated the "pattern" exactly, as did a third! Small 3-shot groups in six different places on the target.
It was a used gun and the Kittery Trading Post took it back without any questions. I checked the crown and that was okay and reamed the forcing cone a bit, which helped a bit, but something was amiss and timing didn't seem to be the problem. I suspect the cylinder boring may have been the problem.