Where are you buying shells for your vintage shotguns? I have searched online for slower non-tox shot shells and can’t find any (20b). Plus most are a mix of steel shot and either tungsten or bismuth. I reload rifle and pistol, but am consolidating calibers to simplify that and don’t really want to add shot shell reloading.
RSTshells.com is the best source in the US for 2.5" non-toxic shells for vintage guns. They sell nice-shot and occasionally bismuth. It's not cheap at roughly $100 for 25 rounds, but how many ducks or turkeys are you going to kill? For everything else, I just use RST lead shot which is far more affordable.