This TC Sidelock Manual PDF indicates the maximum recommended powder charges for their .58 single barrel guns.
One page 77, the maximum load is 120 grains ffg with a patched round ball.
On page 80, the maximum load is 120 grains ffg with a 555 - 560 grain lead bullet.
http://www.tcarms.com/assets/manuals...owder_Guns.pdf
I thought that most folks who strive for target accuracy with .58 conicals limit their powder charges to 60-65 grains. Then let the weight of the lead projectile perform the rest of the work on the game animal.
Accuracy is more important than velocity with large, heavy projectiles and that load should reach out to about 100 yards.