Several people have recommended neck sizing brass in reloading for the lever action 45-70, so I bought a Lyman neck-sizing die for that caliber, neck sized some previously-fired brass, made up some rounds for my Marlin 1895 with three different powders and took them to the range. (As I do with all my reloads, these were also expanded at the mouth with an expander die to help with the seating operation, and then they were crimped with the Lee Factory Crimp Die.)
I noticed two things:
(1) In this preliminary test, my five-shot groups shrank by about 1/2" at 100 yards.
(2) I had some minor feeding problems. The brass was definitely stickier in closing the action, and also extraction was stickier. It felt as if the cartridge was "catching" on something both in chambering the rounds and in extracting them. I could always chamber and extract the ammo just by using a bit more force, except in one instance. That one round stuck going into the chamber, and would not go in. I extracted it, and then tried again, and it chambered without much resistance the second time. (Maybe it was rotated and oriented differently the second time.)
I gather this is why I keep reading that cases should be full-length sized for lever action rifles. Do the folks who neck-size their 45-70 ammo experience the same problem with lever actions? Is there a solution?