Handirifle,
I am impressed with your web link and your work! I have a .375 Big Bore also, and haven't had much luck finding a heavy bullet. At first I "modified" a Hornady 270gr RN with a hammer. That was fine, but no cannelure and they were too long.
Your idea is great. I would love to know your load, though. I am currently working with RL-7 and its fine, but I have heard that AA1680 is better yet. What are your thoughts?