Greetings,
I'll kick my 3 cents (inflation) worth in... Used a T/C .56 smoothbore for my "28" gauge. Using 2 1/4 to 2 1/2 dram loads (roughly 60 to 70gr of 3Fg) and the rough equivalent of #6 shot (or around an ounce). I had no problems out to 30yds, and that's with a "cylinder bore" gun. (I could also use roundball on deer out to about 60yds, 'cause it had rifle sights on it. Anyhow, game was just as dead as with my modern 20. (That's with field loads.)
Only "woosht" it was a little 5 1/2 lb fast handling baton, instead of the extra 3lbs+ that it weighed. That .56 did pretty good duty for me 'til I found a 14ga fowler (which was flintlock like I really wanted), but that's unrelated).
I used empty tomato soup cans to test my loads at every 5yds out to 40yds. I lost my trust in it after 30yds. Your experience might prove a little different.
Have fun and safe shooting!