Welcome to Club 41.
Your 4" barrel will do just fine with Unique, or something in that same burn rate, if you stick with 900-1000 fps and cast lead. That is a comfortable zone for accuracy, recoil and minimal leading with only modest muzzle flash. The "41 Special" loads by John Taffin are enjoyable and economical to shoot. 41 Special brass is available from Starline. If you want to go that way, scrub the fouling from the chambers before loading with full-length Magnum brass cases.
Check your powder cabinet, you may turn up a stray can of Green Dot, W-231 or some other useful powder.
41 Special data is quite handy.
Special data can be used in magnum cases if you seat the bullet deeply and match special COAL. And you don't have to scrub the chambers when you switch back to magnum loads.
