I don't shoot the non-toxic, non-steel shot but I thought they were designed to mimic lead in weight.
As far as your fixed choke, I guess it would depend a lot on the steel of your gun. I shot a 1963 Rem Wingmaster with a full choke from 1978 to about 2003 using a lot of steel shot up to T-shot (once in a while) though mostly 4 to 2 shot. I never had a problem with the choke bulging or anything like that.
BTW I personally think the only thing
steel 6 should be used for is swatting cripples (which it does well) and maybe quail.
