40/90bn

[MikeR]

I don't remember seeing your post in the Shiloh forum about the .40-90 SBN. You might try searching for .40 - 90 or read Dan T's posts, he wrote some on that caliber.
Since you are an experienced BP loader and looking for an CHALLENGE, you're looking at the right cartridge. It will definitely keep you busy trying to figure it out. On some days my .40-90 was the most accurate BPCR that I owned. Other days it was hopeless to get it to keep the velocity spreads below 200 fps. My wife did manage to place in a Creedmoor match shooting that caliber but thank God she switched to a .45-100 SS to save me aggravation. .40-90 SBN'S are also hard to sell so have enough money to pay for a new barrel.