The way I look at it, He has a patent for a collar with 12 guage shells on it. You sell collars with different conchos on them. Just because it looks like a shotgun shell end, it's still a concho.
For a patent, it is very vague. I don't see how you can have a patent that utilizes someone else's patented product, "the cartridge".
Maybe I should go out and get a patent for a "a piece of leather with a mechanism designed to hold up your pants"! I think I'm going to get rich!!!!