I know some one who bought one of those H&R single shot break action shotguns. With this idea in mind to have , a low dollar solution to being able to use all types of shot gun ammo. Aside from 10ga. His thing is "shot guns will be the most useful and important post SHTF gun". So he got an H&R single barrel break action shot gun and barrels to fit his H&R in all the "uninteresting gauges". Since he has several 12 gauges there was no point in getting the 12ga barrel so he got the 3 inch chamber 20ga H&R shot gun and sent it off to get fitted for 16ga, 28ga and 410 barrels. That way if he comes across any non 12ga ammo he can use it as is. I think he said the 20ga was $75 in 1998, then each barrel was $40 plus one time shipping to and from the H&R factory. I think the prices have gone up marginally since then. I still see those H&R shot guns and I think they are between $100 and $120 now.