I've been reloading 41 magnum shotshells for years. Use a cut down 410 wad under a crimped gas check at the case mouth. Shot never contacts the rifling, and I get great patterns out to the fifteen or so feet I've tried it.

Unsure if this is how they do it, but it works for me.

A friend was going to 3D print some 41 shot capsules, but decided my way was easier.