I learned to shoot left handed before I was old enough to realize there was a reason that it could be a problem. Everyone back then thought it odd, as I am right handed in almost every other activity. (Also shoot pool sticks lefty....nothing else)
FWIW, my inexpensive and amazingly accurate Glenfield/Marlin model 75 is never a problem when shooting left handed. Never notice any brass flying, and certainly never a problem with it. I also prefer operating a semi-auto's bolt(when needed) with the forward hand rather than the trigger hand. For lefty shooting, it's "right there".
The only gun that ever was really an issue left handed is a plain old bolt action. Shooting those taught me to shoot just as well either way. But never have tried a left-handed bolt. For some reason it seems to trouble righties when they see me shoot a right-hand bolt rifle left-handed. [boo-hoo....]
Being ambidextrous came in really handy when dove/duck hunting.....no fumbling around, the gun just comes up to whichever hand happens to be holding the grip near the trigger. Winner, winner, duck for dinner.
Many folks never learn to shoot weak-side. It's a great way to separate them from small amounts of cash in a friendly target shooting wager. Don't make the wager too large, cuz they might get angry when they find out you shoot better lefty than righty.