What exactly would you like to know about the 256 Win?
I owned two TC barrels in 256 and shot everything from 60s to 105s including cast. I used the 256 to shoot silhouettes for one season until I advanced to a class where a lost ram was a disaster. I still have 256 junk, including dies, cases, and a box of factory 60s.
Most books advise that you can make 256 from 357 cases, but do not try it. The process requires 2 forming dies and FL die applied in steps. There is some confusion between the cartridge origns, 357 Mag., and what a normal reloader can do within reason.
The 256 is inharently accurate (.5 groups are normal) and will shoot any bullet that can be stabalized by the gun's twist rate. It will digest just about any pistol or small capacity rifle powder. I settled on H-4227 as my primary powder and 87 gr bullets as my primary bullet. My favorite load was 14 gr under an 87. With a scope a 10 inch TC would shoot .25 inch groups at 50 meters. Primers should be small rifle. The 256 is in the same catagory as the Bees, Hornets and 222 for velocity, accuracy and energy with similar bullet weights.
You will find rifle load data at the following site:
Note there is one #7 load shown, but that load is for an Encore single shot rifle, not a Marlin lever gun, watch the OAL and pressure and work up.