Actually it gains a good deal more because it is capable of a good deal more. A quote from Frank C Barnes in Cartridges Of The World, 9th Edition: "Many hunters wished that the 30-30 had a little more oomph. The 30-30 Improved does just that by providing an additional 200-300 fps within the working pressure limits of the std. Win. Model 94 action." Also from Beartooth bullets "The 30-30 Ackley Improved cartridge deviates from the
NORMAL Ackley design in the fact that the shoulder is moved forward when compared to the parent cartridge." Also, again keep in mind that some cartridges have more taper than others, the 30-30 is one of those with more taper. With the more forward shoulder & as anyone can understand, the 30-30 will gain more than most because it gains a higher percentage of powder space than a 30-06 type round & even more yet with a round such as the 308 or 260.
I already provided a chart which shows a
LARGE variance in gains made by the Ackley treatment, some very little & some alot.
And though another example of of how
SOME rounds gain more than others should not be needed, I'll give one anyway. Take a lookie at the Sierra Manual #5. Take a lookie at the 6mmRemAI and look at what
SIERRA has to say about it & I quote "In the
example of the 6mm Remington, the excessive body taper & gentle shoulder design provides
SUBSTANTIAL room for improvement." Sierra's words, not mine.
But back to the original question.
Unless you are a serious Target/Tactical shooter, I don't believe I would AI the 260. Because of the lack of taper & small powder increases of this round, I doubt the value added would be much at all.