BB's for air guns are just under or at .177. They, for the most part, are copper plated/washed steel, or non-plated steel as well.
BB shot for loading in shotshells is .180"(usually) nominally and contain 50 pellets per ounce in lead.
I bracketed the word usually due to odd times, different mgr's have slightly different sizes, per shot # or name.
Typically BBB is .190" as well, with "T" being .20".
The larger the shot, the larger the "holes" between the shot pellets in the pattern, which makes wounding rather than killing much more likely.
You will need to pattern them to see if they will be effective. I would suggest, that BB is a poor choice for shot for turkey, from a muzzleloading
gun without choke. One thing they will do, is drag feathers into the meat, most likely.