varation on 25-20 lever

6Pt, I would try the anneal and size die, if that doesn't work it sometimes helps to give your seating die a light polish using Flitz or any of the other very mild polishing compounds. Some will tell you to turn the seating die in one half turn at a time but I find ¼ turn at a time works best with my RCBS die. I have formed 256WM from new brass both annealed and as they come out of the bag and it didn't make a lot of difference for me. It just takes a lot of die turning. A form die is a good plan and they are not terribly expensive.

I have experienced very poor case life over the years with the Marlin M-62 rifle. The problems with the case are well known. The Marlin and the standard Thompson Center chambers are cut a bit long from the front face of the rim to the point of the shoulder. The rim thickness on the .357 Magnum cases vary a bit in thickness and this causes problems setting up your die for neck sizing as not all of your cases will chamber and allow the action to close after the cases are neck sized. The .357 Magnum brass is not designed to work at the upper pressure levels of the .256 Win Mag and the cases stretch a good bit. You need to be careful in lubing the inside of your case necks for sizing as in my experience the neck expander will stretch cases quite a bit if they are not well lubed. When I load the .256 Win Mag with maximum published load data I seldom get three loads from a .357 Magnum case fired in the Marlin Model 62 rifle. Lighter cast bullet loads work reasonably well.

On the positive side the Marlin Model 62 has proven to be a very accurate rifle.

Back when the Marlin Talk board was going strong Greg Mushial and I spent a bit of time playing with our .256 Win Mags and .25-20's. Greg bought a Marlin .25-20 barrel and had it re-chambered to .256. His chamber was cut very carefully and he used .256 Winchester brass. His case life was excellent and his accuracy was just a bit better than mine.

I like the .25-20 and concentrated on it for a few years and now I have met a young fellow who needs some assistance loading for his .256 so I brought things out and bought a form die. As you can see from the picture it is easy to break cases. These push out with a .30 caliber brush without difficulty. It is best to use a pistol brush as you don't have much room when the bolt is open. I use a brush which has threads too small for my rod. This way I can push the brush down the barrel and bring the case out of the chamber and push the brush and broken case down through the magazine well. If you shoot your Model 62 you will break cases so be prepared. I am forming a few rimless cases from .223 Remington brass and I will form a few from .357 Maximum to see how they handle pressure. I expect to have to inside ream both cases. My Marlin Model 62 will extract but not eject the rimless case. Not certain why.

I look forward to exchanging some cast bullet data as you get ready to shoot. If you want to talk about jacketed stuff we can start a thread on Beartooth.