Matrix: I use a Rem870 Marine Magnum that has the following mods. - Syn. regular speedfeed stock/forened, Sage ghostrings w/tritium front bead, sidesaddle, and a Giles sling. It also has porting from a local smith, which works well with decreasing muzzle rise. I have shot it in total darkness to compare with an unported (but backbored) Vang Rem, and the muzzle blast is less than the unported version.
I started with two plastic Safariland shotshell (holds 2 each) holders, and then also purchased a shotshell holding nylon belt I wear above my regular belt.
I usually shoot the Sellier and Belliot 00buck, merely because of price, it's economical. I back it up with reduced recoil slugs usually, in the 2 shotshell holders, or a couple on the sidesaddle.