This thought had crossed my mind,but,for me,I do not think I will pursue it.
As I understand how it all works,the 38-40 and 44-40 ,with the thin brass and shallow bottleneck,could feed up into a lever action chamber well,and the brass obturated very well to keep the black powder fouling forward of the case mouth.
What I was wondering about: Necking down modern,strong 45 Colt brass to feed a .44 magnum barrel.Rim size is pretty much the same.So,this would be a hot rodding effort.
In theory,some case capacity could be gained,and turning the corner into a lever gun chamber would be easier.Mag tube would be the same.
On balance,a straight sided pistol case is real easy to work with.Ideas!!Get a lot of them,life and money are too short to chase them all!!This one did not make my list.