Life Line Warrior Medicine is a left handed Canadian who has some videos about firearms. Yes, people in Canada have firearms and while they have stringent magazine capacity restrictions they do not have restrictions like a barrel being too short on a firearm.
Ryan James shows how he does combat reloads using a short barreled Remington 870. The 870 is decked out by S&J Hardware and has an Aridus Industries QDC side saddle. However Ryan is using a normal right handed Remington 870 but left handed manipulation. I tend to prefer having my shells brass down as a right handed shotgun shooter. That way I use my support hand to cup the round up into the chamber.