I have 4 and my shooting friend has 2 450 BPE 3 1/4" case double rifles. All 6 guns have enfield or standard rifling and we use commercially cast .459" 300-325 grain GC bullets. We follow Wright's suggestions on page 219 of his third edition data with Kynoch foam filler wads to keep the powder against the primers.
I have chronoed these loads at speeds up to 2000 f/s.
A 1869 Rigby hammer double shot great 25 yard target, held center. Lighter load of 45 grains 4198 and 325 grain bullets. About 1900 f/s at 19.5K pressure.

A 1890 Holland double, first shot held center, hit high next three held on the quarter hits all centered. About 2000 f/s at 23.1K pressure per Sherman Bell's testing.

Get a hold of Sherman Bell's articles "Finding out for myself" that pressure tests factory NFB loads
at 25K pressure and reloads using 4198, RE 7, 3031, and 4064. He tested the factory 120 grains of
BP loads at 21.6K pressure. And his article on use of 14 types of case fillers used in NFB loads.

The Rigby:

The Holland: