Ackley improved ?

[PJ]

Guys,
I have heard of AI chambers before. What i wanna know is how EXACTLY does it differ from the regular chamber. "I.E.: Shorter, Longer, less taper, more taper."? Thank you for any info you can provide.


PJ

 

[BoydAllen]

AI stands for Ackley Improved. These cartridges are larger capacity versions of standard calibers, designed so that the standard version of the cartridge will headspace at the neck shoulder junction of the case. When the standard case is fired, it takes the shape of the AI chamber, which has a steeper shoulder angle, and less body taper. From that point on the case is reloaded with AI dies, and because it has increased volume, may be loaded to a higher velocity than the parent case. Some reloading manuals have reloading data for the AI cartridges and show the dimensions. Usually, the smaller the parent case, the greater the percentage increase of velocity by going to the Ackley version. Parker Ackley's Vol. 1&2 of Handbook for Shooters & Reloaders tells all about these and many other wildcat cartridges.

 

[trappst]

Normally, less body taper and a 40* shoulder angle.....

This equates into less case strecth when sizing and more powder capacity. For the two ackley's I have, cases will shorten a very small amount upon fire forming. Fire forming brass is simple and usually gives very good accuracy. From there, load and shoot as normal while taking advantage of the new case!

For your viewing pleasure,left to right): 22-250 rem, 22-250AI, 223 rem, 223 AI

Click to enlarge

 

[Cheechako]

The above very well describes the Ackley Improved cartridges. But P.O. Ackley designed a LOT of other cartridges too. The name Ackley on a cartridge could mean a lot more than a blown out factory case with a 40 degree shoulder. And P.O. had nothing whatsoever to do with many of the Ackley Improved cartridges. The designers simply stuck his name onto them.

Ray

 

[PJ]

Guys,
When you go with an AI does it mean you lose OAL of the case? Do you move the shoulder back and change the angle? Just trying to wrap my mind around this change to the case.

PJ

 

[Cheechako]

pj

If you look closely at trap's photos you will see that the dimension from the base to neck is the same length but the shoulder angle has been increased and the case body blown out to less taper. To get less taper and a sharper shoulder you need a little extra brass and it comes from - yes, the length. The case will only shorten a little, maybe .020" or so if the forming was done correctly. If you get an AI case that is the same length or longer than it was before you fireformed it, that means the extra brass came from somewhere else, like the solid head or case walls, and that is not a good thing if you want those cases to last very long.

Ray

 

[PJ]

Ray,
Is the chamber cut a little shorter for the AI then the standard? I think the bolt thrust is less on the AI then a standard. Is this because of the taper being changed?

I'm thinking the AI increases the wear on the barrel. If so by how much? Does it make sense to have two barrels cut with the same reamer. By the same smith. Use one to fire form and the other for the rest of your shooting.

PJ

 

[Preacher]

The Ackley chambers are usually cut to .004 shorter than the parent case so there will be no headspace problems while fireforming them. At least a 360 turn on the barrel is required but that needs to be checked on each individual barrel....
The increased velocity will wear the barrel a little more but not enough to not take advantage of the improvement they make.....
Lots of people use a dedicated fireforming barrel, just be sure they are exactly the same, not just pretty close but EXACTLY the same......

 

[ROCKJAG4]

BETTER YET...USE THE "cream of wheat method'--no bullet,-no wear on the bbl, this method '''works great...try it..

 

[Cheaha]

Most "AI" cartridges are not "AI" but just "I". That is, P.O.Ackley didn't design them, somebody later just improved another cartridge and stuck the "AI" on the end of the name. Some of these don't have the 40 degree shoulder but 30 for example. Most improved rifles that I have seen use a crush fit to chamber a virgin case. My 7mm-08 AI doesn't gain much velocity over the std 7mm-08 but does look cool and reduces greatly the need to trim. Everybody needs at least one "AI" rig.

 

[2644ever]

And P.O. had nothing whatsoever to do with many of the Ackley Improved cartridges. The designers simply stuck his name onto them.

A case in point,no pun intended) is the 6.5x55 BJ Ackley Improved, the brainchild of famed Precision Shooting's columnist Bob Jourdan. Bob carefully measured all dimensions on every actual AI case he could locate, in order to find out what was consistent in the Ackley design,taper, neck legth /body length ratio and so on)before ordering his reamer.

 

[SongdogHunter]

Everybody needs at least one "AI" rig.

I think so too thats why i went with a .243Ai and 257 Ackley.

Michael