I have always had a hankering for a LR ML.
Vic said a lot in his post.
Heres my SAWG (Scientific Wild Arsed Guess) based what I have observed, discussed w/ others, & read.
A LR ML rifle is expensive & hard to come by. It will shoot w/ the best of them. You just need the Really Big $$ to find an original. Or, pay the Big $$ to have a skilled gunsmith build up one w/ the false muzzle, loading tube, bullet mould, die, or swage, right barrel & twist, lock, possible patch cutter, etc. Finding someone who is skilled, willing, & able to do the work is another problem.
One thing bout a cartridge rifle is that the Shooter doesnt loose the range conditions, esp. light & wind. & A good Shooter will take advantage of range conditions w/ a cart. rifle to fire maybe 2-3 rounds while the ML is loading.
However, w/ a ML, the Shooter must take the time to reload, & often this means loosing the range conditions. Also, it appears shooting a ML is physically tiring, esp. in warm weather. The Shooter must get in & out of position ea. time to shoot & reload.