I'm thinking Firing Selection, Personalized Grip, Powered Folding Stock, Underbarrel Weight, and Increased Cylinder might be the way to go - RC3, so even with Possibility 3 that's only a -2 penalty for the second shot, which with this thing's damage code wouldn't be so bad - and what's especially important here: all of that save the Increased Cylinder requires only a Kit or Shop; Personalized Grip does require Artisan, though, so those two might need to be done through contacts.