Yeah, capacity always wins. The .257 Roy has about 80 grains of case capacity, the .25-06 AI about 65.
According to the 1/4 rule (which was stated correctly by somebody on this thread) the .257 Roy will therefore get close to 6% more velocity than the .25-06 Ackley AT THE SAME PRESSURES.
That phrase is capitalized because it is important. Yes, you can get .257 Roy velocities out of the .25-06 AI, but only at much higher pressures. This is generally the trick with making an AI cartridge act like a bigger round: load more powder.
At equal pressures the .257 Roy will beat the .25-06 AI by around 200 fps, depending on the load. Thus if somebody is stoking the .25-06 AI white-hot and getting 3600 out of a 100-grain bullet, then the same "loading technique" would get 3800+ out if a 100 in the .257 Weatherby. And some people do. It's that simple.
It also isn't magic. It's just pushing the cartridge beyond the standard limits. Whether this is smart is debatable.
Lotsa wisdom here.
The handloader can sometimes make a smaller cartridge give the velocity of a larger one ... but the increased chamber pressures significantly reduce the safety margin of both the brass and the action.
Who needs primer pockets that loosen in a couple of firings and pressure that is "iffy"??? Surely not me. I've survived one rifle blow-up and absolutely do not wish to over-tax my Guardian Angel.
If you need the added muzzle belocity, get a larger cartridge.
That's why I bought my Remington 700 SPS .257 Weatherby. I have a perfectly wonderful gain-twist .25-'06, but the .257 Weatherby will absolutely, positively do it "gooder."
Steve
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