Your "stalking rifle" is a reworked '71? Original loads will work best, PP with generous lube cookie. I hate PP'ing. I use RCBS 44-370. It drops around .448" +/-. Groove dia is up around 451+. Any boolits that big will not chamber for me. C&H have dies I call correct in that they size and expand for a .446 ish boolit. Others may not. The Lyman 446 is OK, I think they changed it a tad and the new don't work so good. I think RCBS made a 43-370 as well that drops about .439. You could go with powder coating and give us a full report. best of luck