So I bought a Ruger #1 in 450-400 Nitro Express. The least expensive ammo I could find was...$89.00 for 20 rounds. Yep, almost $5.00 each. British African cartridges are expensive! I emailed Hornady and they said they should make a another run of brass in July. I sure hope so. Even that should be about $36.00 for 20.
NOE has a great looking boolet I'm going to try, the 412 360Gr. FN GC. I found some loading data that shows 32Gr of Accurate 5744 throws a 400Gr boolet at 1300fps. While 49Gr throws a 300Gr boolet at 2100fps. I'm going to try and find a happy medium. It seems that 5744 is the way to go.
I have some .410 265Gr GC boolets that I'll mess with a bit. They're likely too light but maybe they'll be good for target practice.
..stay tuned.