I recently got a Mountain Molds "375BP300" mold on ebay.
The thing that this mold cavity most closely resembles (in my unlearned opinion) is a 'flying brick" (with grease grooves, of course.) I'm assuming that the BP stands for 'black powder', and wondered whether you used any different design criteria for BP molds vs. smokeless mold designs.
My primary intent is to cast these hard and load them in my Win 70 375 H&H.
Curious to know (besides absence of gas check) if you could provide any specifics for this mold (ie: have you made a lot of them, or was this a 'one off' mold).
I've also thought of trying the 'Wilks Gas Check' approach and center-drilling out a hole in the GC the size of the sprue hole, annealing the GC's, and inserting said GC in bullet base when casting to try to up the velocity above 1600 fps ceiling for PB bullets.
Haven't received the mold yet, but from the looks of it, it may proved to be quite the 'thumper'.
Any and all suggestions, recommendations, and/or other illumination would be appreciated. Thanks.