I believe all leverguns in pistol cals have long throats. The accuracy potential is further exacerbated because cases have short straight walls. As you have found, you can't design a bullet that meets our "usual" criteria for cast bullet accuracy and still cycle in a levergun. Add to this maybe a loose chamber where the bullet will slump towards the bottom of the chamber and you have a recipe for poor accuracy potential. Lead bullets, even ones made from hard alloy, are softer than their jacketed counterparts. Being harder, jacketed bullets are better able to withstand the vagaries of alignment and still provide some semblance of accuracy. Its more difficult to obtain accuracy with cast bullets under these circumstances.
After a great deal of trial and error this is how I approach cast bullet loads for these rifles. Firstly I use as wide a diameter bullet that will just chamber, ie the loaded cartridge needs to be a snug fit in the chamber. This way the snug fit provides alignment of the bullet with the bore.
I use a bullet that has a body that is able to reach the rifling before the base of the bullet has cleared the case mouth. In the case of the 44 mag, the throat length is around 0.22", so a body length of at least 0.25" should be sufficient. Upon ignition the bullet transitions through the throat aligned with the bore (because of the snug fit in the chamber) and remains supported until the bullet enters the rifling. When the base has cleared the case mouth, the bullet has already entered the rifling and has been supported during the transition.
Anyhow that's what I do and it seems to work.