I use loaders that are held on my gun by a standard 12 guage shotshell holder. I got 2 (50gr) pellets and a 250 gr Shockwave in there and it works well for me. You can put a 209 primer in the end of your stock if the end is made of rubber.

http://i126.photobucket.com/albums/p119/gotbuck1127/Hunting/Gun.jpg