The US army issued buckshot loads for their .69 caliber muskets, having 9, I think they were, 00 buck.(.32")
These "loads" were in paper ctg. form, so I assume there was some sort of divider between the powder and shot.
The reason, I suspect the why of Smylee's question, is that some people call all shot sizes, "buck shot".
Lead Buckshot size names, depended on the country (I assume) or maker and usually ran, #4 #3, #2 #1. 0, 00, 000 as well as SG, SSG.
BB is not a buck shot, but a heavy bird .177" and also suggested for fox shooting. Back in the 1960's, #4 was .280" in diameter. Today, it is
.250" seems to me. Taylor uses it in his .25 Flinter.
Some commercial buck shot is hardened with 3% to 5% antimony and some is pure lead. Too, the sizes sold today, are not all true to the 'old
sizing charts'. An example of that is Hornady's 000 buck, which they sell and is .350", whereas 000 buck in the old charts, is .360" in diameter.
In guns without chokes, patterns are usually dependent on the type and arrangement of wad columns.