For the most part the reduced taper means reduced case stretch and thus less trimming required. Also holds the chamber a bit better so in theory at least in a TC you can stand higher pressure. Same with any gun mostly limited by back thrust rather than just pressure. Case life will be improved some and you'll usually gain maybe 100 fps.
I have had some experience with the Ackley line of improved cartridges. I have had a 250 AI, about a dozen 257 AI, a couple of 7MM AI's and 4 '06 Ackleys. The improvement is much more pronounced in the smaller case as opposed to the 06. GB is correct in the increased case life and it is by a considerable margin. Also a large majority of the rifles I've had showed some improvement in accuracy, the lone exception was in the '06. It didn't change the grouping in any of the 06's. The smaller cases suddenly became less "fussy" to load for. Regarding the velocity increase with improved cartridges, the smaller the case the greater the gain. MY 250 showed about 200fps gain, the 257's about 100 to 150, the 7MM only about 100 and the '06's not any measurable gain. The '06 just required more power to reach the same velocities. It did allow for the use of slower burning powders however. The real drawback has been almost all actions (bolt) will have to be altered to feed without problems. :?
I have three Ackley Improved rifles. One 22-250 AI that I get 220 Swift velocities out of and two 250 Sav. Ackley Improved. I have had the one ( built on a Sako action) for a couple of years and love it. The other (Rem. model Seven Stainless Synthetic) I just got back from Olympic Arms. I haven't shot it yet. One thing I did notice is that even the brass that I full length resized, won't chamber in the new one. I'm anxious to fire-form some in the Rem, and measure the difference in the fire-formed cases. I could understand the brass that I mearly neck sized not fitting, but the full length resized cases should have chambered. I'll have to wait till I get a day off and shoot it. The 250 Sav. AI is a great caliber.
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