I am left handed. I have shot the following weapons, all from the left shoulder (or left hand):
*: while in the army
Although I have to adjust my techniques to accommodate for right handed designs, I am able to be efficient with all of them. I qualified with all weapons in the army.
If you believe some posts on the Internet, I should have gotten a face full of shells. Never - not even once - did I get a shell in - or close to - the face. Even when I was shooting blanks in the army, from all sorts of weird positions, it never happened once!
In fact, the only weapons I will not shoot from the left shoulder, without reversing the ejection (if possible), are bullpup rifles. I tried once with my Tavor, I'll never do that again!