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For the 85 grain gas-checked 257312, it lists a maximum load of 10.7 grains of 4227 producing 1750 fps.
Bullets were cast (BHN ~12), sized .258 and lubed with home-made Moly lube.
Test loads were assembled using R-P brass and Winchester small rifle primers.
Case mouths were flared using a .25 caliber flaring die (from a .25 Hornet die set).
A little extra velocity may be helpful (but not necessary) in that it flattens out the trajectory and gives a little added range, but it wont promote the cartridge up to being a good deer cartridge.
Bottom-line -- the .25-20 is good for shooting bunnies, skunks, porcupines, coyotes, etc. Whether the intended quarry is intended for the dinner table or simple extermination, will dictate the nature of the bullet/load.
A philosophical aside -- theres no real reason to try to hot-rod the little .25-20, because no matter how hot you load it, its still a small game cartridge, so it makes sense to stay within the SAAMI guidelines.The beauty of the .25-20 is that it can handle both of these tasks with ease.