A close friend of mine is very much into shooting black powder in his lever guns. For all the reasons above he prefers the 44-40 over the 45 Colt. Mainly however the 44-40 seals the action better against the black powder residue and is therefore easier to clean after shooting.
The reason it seals better has to do with the thinner brass and the shoulder. This also makes it more difficult to reload.
He has a 45-90 lever gun and anneals the cases to make them seal better.
As far as accuracy, a couple days ago he shot a coyote through the heart at 200 yards. One Shot!
Today he missed a coyote at 500 yards. Distance was fine but didn't allow for windage. He was resting the rifle on the top rail of the fence.
