Mik 1,
I have used 4 different cast bullets in my original 1873 .44 W.C.F.
The 200 gr. Lyman Cowboy bullet, 200 gr. Magma, Lyman 427098 and the 200 gr. bullet from an early Winchester mold. All shot well. Alloy used was wheel weights + 2% tin. I have not tried the 200 gr. RCBS, but Mike Venturino recommends it highly.
For smokeless, I would stick with the bullets that have a crimping groove... 200 gr. Lyman Cowboy bullet, 200 gr. Magma, 200 gr. RCBS.
For black powder, the Lyman 427098 is THE bullet. It also works very well with smokeless, BUT unless your resizing die will produce a neck that is slightly longer than the seating depth of the bullet, or you use a capacity load of slow burning smokeless (REL 7 works well for this) this bullet can telescope into the case under spring pressure (and recoil) from the magazine since it is designed to crimp over the front driving band.
Have fun with your .44-40.
w30wcf