It's reamed out to a 40 degree shoulder and holds more powder. If you are a reloader, the cases last forever. You should get 100 to 150'/sec increase in velocity in the 25-06. The 257 Weatherby Magnum has no ackley version ( to my limited knowledge) becausethe neck and case have already been jibbered with....so the bottom line is the 25-06 is real close to the Weatherby.The Ackley modification has the biggest bang for the buck in .257, 7mm Mauser and 6.5-'06 calibers. The 25-06 will definately perform better when Acklied. One of the great myths is that the 30'06 Ackley doesn't do much.....oh contrair....I get 150'/sec faster speeds out of mine without extreme loads. You can "hotrod" anything, however the Ackley allows you to increase velocity without going to high chamber pressure thereby increasing barrel life and making your rifle a flatter shooter. That's my 2 pennies. For 100 dollars or so, that's a good cost effectiveupgrade. Regards, Rick.