Hello TC,
If your using Black Powder use a lighter bullet, do not reduce the powder charge volume, air space inside a BP cartridge is very dangerous indeed.
Try and obtain some correct length brass,or some .577 x 3" basic cases, and cut down to length. None are cheap but you won't need more than 30-50 cases and they will last you a very long time, if you pay attention to cleaning them after every use. Not many folk like to fire more than 20 or so rounds in any range session.
I'd recommend you don't use short shotgun brass, as on firing lead bullets 'bump up' and you'll soon find that there is a ring of sheared off lead between the end of the brass case and the start of the rifling, the bullet is going to have to jump more than 1/4" from the case mouth to the rifling. Your accuracy will probably be better if you just threw the bullets at the target.
Shotgun brass is all right for making the .577 Snider case but that is shorter then the 24 gauge brass.
I've shot .577 Snider, .577 BP Express and .577/450 Martini-Henry rounds for over 40 years. All in full military or hunting specification loads, so have a fair bit of experience in loading these rounds.
Bill Flemings book 'British Sporting Rifle Cartridges' gives 11 different BP loadings with bullet weights ranging from 480 to 650 grains with powder charges (Black Powder) ranging from 135 to 176 grains for this cartridge.
There's really no such thing as a light plinking or target load with a .577 round irrespective of case length.
Get your cases the right length and use correct loads and have fun.
Harry
