In the 1990s, Ted Fellowes, Les Orestad, and I were shooting the production prototype Ferguson rifle Narragansett shipped me, at Ted's Issaquah, Washington, range. Les and I shoot left-handed; I also shoot rightie. One shot with the Ferguson - left-handed - and I was certain that I would not shoot a rightie flintlock from the left shoulder. Les concurred. Recoil caused us to inadvertently and slightly inhale. Not pleasant. But shooting rightie was no problem.
I shoot Sharps 1863s leftie without any issues. Les shoots several rightie cap lock rifles, again, without any issues.
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Parenthetically, In Donald Dallas' excellent book, The British Sporting Gun and Rifle, are photograph and blurb describing how Alexander Henry built his dropping block single-shot rifle actions for lefties with the lock on the right side. He - and I - believe that side lock dropping block actions are easier and quicker to load when lock is not interfering. After several years, Henry ceased making his leftie dropping block that way - mostly because buyers were expecting side lock single shots to "look" a certain way. If you want a beautiful visual of what I mean, in "Quigley Down Under" watch Quigley load and fire when he demonstrates his proficiency to the villain near the beginning of the film.
