.30-40 Krag brass always works well to make .40-50SS brass, but I had issues with some .303 British brass that was slightly large at the base diameter. Can't recall the brand, but I stick with .30-40 brass ever since.

In the short time I have had this very nice little rifle I have developed four solid loads for it that will collectively cover the full range of its useful purpose.
#1
case --- PPU 303-B
bullet --- Lyman # 412263, 300gn, BHN-8, .408", NASA lube
primer --- CCI# 350 LPM
powder --- duplex .3cc Accurate- LT-30 under 35.5gnH-870
FPS --- 1358, 1346, 1358
note --- very accurate

#2
case --- RP 30-40 Krag
bullet --- Ballard 325gn paper patch BHN-8 wet wrap Southworth 9lb .4085"
primer --- CCI#300 LP
powder --- duplex 3cc Accurate LT-30 under 39gn scale weight FFFG
one 1/8" nitro card wad under NASA lube wad
COAL --- 2.690"

#3
case --- PPU 303 B
bullet --- Ballard 330gn pure lead PP Southworth 9 LB paper .4085"
primer --- CCI#300 LP
powder --- 14gn Alliant 410 + packing popcorn filler under NASA lube wad

#4
case --- RP 30-40 Krag
bullet --- Lyman # 403169 250gn BHN-7.5 .4075" NASA lube
primer --- CCI# 300 LP
powder --- 6.2gn Lightning
note --- Lightning is a name I have given to an Aussi powder that has a long number description that I cant remember. In burn rate through testing it seems to be right between Unique and Herco.
note --- very accurate short range load great for small game.

We have now added 40-50 SS brass, bullets, and ammo to our list of offerings from The Bullshop