Envirometal can pound sand AFAIC
Small TSS shows the most lethality in 20ga, period. Bismuth does very well, and approaches lead in 4/5/6 shot. To 40 yards, fast steel 3 & 4 shot has killed most any duck I put them on. It’s better to front half them, no matter what gauge and shot. It’s not harder to kill them with a 20ga, it’s harder to get the pattern in the right place, with the right density. All else being equal, shot doesn’t care about gauge.