I'm glad you explained that, but has lead shot ever damaged WS1 barrels? I might be wrong, but I've never heard of it. Winchester proof tested their barrels to several times normal loads and there have been many WS1 guns made over the years and a lot of rounds of skeet have been shot through them. But then again, I might be wrong. I never heard of people feeling that way about WS1 chokes. Maybe, I won't be so excited about buying skeet guns from now on. So, thanks again and good luck.
I'm sure steel shot can be shot out of a M21 without adverse effects provided you don't have chokes tighter than modified. But, I have no plans to find out with my nearly 90 year old M21.
