Obviously, not using steel shot in a fixed choke older gun.
Why would you want to shoot steel in a really light upland gun?
I'll shoot Bismuth for any non-toxic shot required.
A few boxes of Bismuth shot loads, or handloaded, are no big deal with the price of fuel, accommodation, and other costs of hunting these days.
Light is an absolute criteria. It's light or it's not.
My choice doesn't have to be anyone else's.