<slight departure>
"Like 230RN, I'm curious as to what guns use left and right-twist rifling."
I think most original Colts (at least handguns) are left-hand twist. Non-Colt variants are usually right-handed.
I strongly suspect old Sam'l Colt was left handed, but can't confirm it. But if you've ever handled an SAA, you will realize that it's a lot easier to handle (eject, reload) if you're left-handed. I also suspect the left-handed twists of his handguns are a subtle "dig" at right-handers. (See ETA)
People sometimes complain about the weird recoil of the (milspec, original) 1911s, and I further suspect that this is because of the gun's Newtonian reaction to the left-handed twist* --which would make the gun's "twist recoil" to the right, clockwise, instead of to the left, counter-clockwise.
No need to respond, just sayin'.
</slight departure>
Terry
* Yes, Newton's third law (action-reaction) applies to angular momentum ("torque") as well as linear action-reaction.
ETA: The counter-argument to this is that handguns, both aboard ships and with the Cavalry, were intended to be used with the left hand, with the cutlass, saber, or sword (the primary weapons) wielded with the right hand. That's why images of the Cavalry have their holsters "backwards" on their right side --for crossdrawing with the left hand. Folks go back and forth on this, though.