I bought one, I think uncle mike's. Dont think it said what gauge its for but put it on my 20g that I have standing next to the bed for home defense. got 5 buck shotshells in it. Cann't attest to how it would work in the field, but it holds the 20gauges pretty secure and imo would wok fine in the field. Hope that helps. They had mine at local sporting goods store.

http://www.uncle-mikes.com/products/buttstock_shell_holders.html