AI cartridges P.O. Ackley Improved cartidges

AI rounds can increase your velocity with more room for powder.

Most AI cartridges keep the neck angle.  But some have variations on the neck angle.   250-3000 has a 40 o version that some use.

Yes, taking the body taper is the main definition of AI improved cartridges.  P.O. Ackley did it mainly to reduce bolt thrust, but he also discovered it gave more capacity and on some cases gave less case stretch. 

Changing the angle does help increase the capacity, just a very little.  But again, Ackley was looking to reduce bolt thrust (the force the brass exerts on the bolt face), and the angle change does that...to a very very small extent.  

I have PO Ackley books from the 60s, they are little spiral bound books, very cool. Anyhow, he started, of course, with the military rounds of the time for obvious reasons. He found the 7X57 family had the best results the reason was they were heavier tapered and a lesser neck angle than the 30-06 type. There was a good reason for the original design taper and slight neck angle, ease of feeding from a magazine and more reliable extraction from a military bolt action rifle. However, as the American public became more enamored with sporting arms (Post WW2) the "combat reliability" was less of a necessity. Thus began Mr Ackley's work. The 250AI, 257AI and 280AI became the most popular with the advent of modern slow burning powders. The 308 family had little to gain from the body taper and neck angle because they already were very close to the AI form. When I had Jim Hart build my first rifle, I talked to him about a 260 or 7-08AI. He said you are gonna mess round fire forming brass for very little gain...noted. PO Akley was way ahead of his time with his work. A perfect example of invention out running the technology of the time, the slow burning powders that made the AI shine were not even invented yet, but it seemed he knew someday it would catch up.

Edited by MapleHill - 09 January 2025 at 15:56

I totally understand that faster is better but I usually find the best accuracy at less than max velocity. 

That's an impressive group at 100 yards. That's an exceptionally impressive group at 200.

 Bear it's sighted in for a 300 yard pointblank range, so she doesn't have to adjust her point of aim.

Wing, We have also find we pick up around an extra 100 feet per second from identical loads with no more presser issues, Maybe even a bit less recoil.  

Correct.  that is why they operate at lower pressure; although one can add more power to get them up to SAMMI pressures and increased velocity.