If it chambers unsized, i.e., if a dummy round loaded to the correct OAL will chamber, don't size it.
When loaded with BP, my rifle loads are enough powder to give me ~1,300 fps with OAL ~2.80". For shooting in a rifle, my carbine loads are ~2.42" with enough powder to get ~1150 fps; out to about 300 yards that matches up fairly well with the 1879-pattern sights on my rifle. No wads. Carbine loads are compressed by the bullet, rifle loads I'm using a compression die.