If you fnd that 28 gauge in ball or buck is difficult to find, the muzzleloading folks may be able to help out. A .54 caliber round ball, either .520 or .530 (depending on the inner diameter of your barrel) will work very nicely as a slug in a .28 gauge. For buckskot, it is recommended you go to #4 buck, They are .24 caliber and three of them will lay nicely so you can stack more buck shot on top. If you use too big of a buck shot, you can only load a few and have lots of open space between the shot balls.

As a particurlarly effective buck shot load, you can put in split shot like when you crimp on your fishing line. When they hit something, they will butterfly out making them bigger, or break apart giving you multi-projectiles from the same shot load. If you don't find any factory loadings for buck or slug, you may have to open the crimp on some factory shells, save the shot and put in its's place the small buck shot or single ball or slug.
Ohio Rusty ><>