Speaking as a very left-handed person, I can say I never really felt at a disadvantage using a right-handed gun. I grew up shooting a Mossberg 500, which tossed the empties across my face, no problem. Concentrate on the target.... The tang safety on the 500 was a nice touch, but the Remington ads of that era touted how their cross-bolt safeties could be reversed, and Ithaca's 37, well, you know.
Similarly, my M16A1 had a brass deflector so, other than the occasional hot empty going into my right sleeve, I had no problem in my military shooting. I wasn't an M60 operator, so the few times I did shoot one, I think did it from the right and tried to walk the rounds in.
And my sxs are all righthanded. I can't say I'm the greatest of shotgun shooters, but I know I have broken 25/25 (well above my average) shooting trap with my very right-handed (English stocked) Simson, so I suppose it's more operator error and in my head, than in my gun.
The two places I can see having problems shooting RH are (a) bolt action rifles and (b) German guns with a "baecke" cheekpiece. The former are a pain in the butt, which limits my selection in rifles. The latter, the cheekpiece winds up being added dead weight. I've seen about 1 gun with such cheekpieces set up for a lefty, for every 100 for a righty.
YMMV.
