I recently started spearing as well. I shot my first AJ in the Gulf this past weekend, it was a blast. I have a 42". 2 band JBL, and while it gets the job done, I don't always get full penetration which can lead to lost fish. I wouldn't recommend trying this with bigger fish that could wrap / drag you, but what I do is take the spear and (without holding the fish) push it into the fish as fast as possible. The pressure of the water will slow the fish's movement down and allow the spear to go all the way through so that you can remove it easier and finish the job if it's not already shot. I have to do this often with catfish, but have also found it effective with a Triggerfish and a Grouper.
As far as the bruises from loading it go, that's just part of it at first.. You'll get more comfortable with it as you spear more, but I tighten up my abs, and put the butt right on my pelvic bone.. That helps me alot and makes loading a lot easier.
Hope that helps. Good Luck.