Ok, thinking about building a new rifle in 6mm Rem., but I've been reading a lot about people using the AI version. I'm definitely ignorant in this area, so why would I want an Ackley Improved anything? I see a lot of 223, 22/250, 243, 6mm and 280 AI's. I've read about better case life, etc, but having to fire-form brass sounds like a lot of work to me, but the AI sure does look sexy. So, why do you AI?

No case trimming, about as much increase in speed as if you had a really fast barrel in a standard chambering, a bit less backthrust if this is a concern (thompson contenders est.), and last at least for me, IT JUST LOOKS COOL!!! I shoot a 35 Whelen improved, a 250 savage improved, a 7mm-tcu like an improved, and a 309jdj again like an ai improved just designed by someone else. You will gain a bit of speed, but only you can decide if it is worth the extra trouble. You will also likely lower the resail value of your gun over the standard chambering. You can fire standard loaded brass in an improved chamber, and accuracy is usally very good, with little velosity loss, and get perfectly fourmed improved brass.

Some of the AIs are worthwhile, others are not worth the extra effort - most are just mild improvements. I don't buy into the greater case life, improved accuracy, or greater tolerance to higher PSI. Brass is brass, and it will start stretching beyond its elastic limit at about 63,000 PSI and higher, no matter the case design.

Nonetheless, if you have bunches of certain brass or a 30/06 equivalent action, and you'd like to rechamber, you might consider certain AIs. I have a 257 AI, 25/06 AI, 280 AI, and 30/06 AI.

The 257 AI and the 280 AIs are significant improvements, but the other two are only mildly improved at most. The 257 AI performs roughly equivalent to a 25/06, whereas the 280 AI will approach 7mm Rem Mag performance - all with roughly equivalent PSIs. The 25/06 AI is well overbore and not recommended.

If you have tons of 257 brass you might consider a 257 AI, and if you have tons of 270, 280, or 30/06 brass you might consider a 280 AI, which I believe is about perfect bore for 7mm, given current powders. IMO the 7mm Rem Mag or greater mags are well overbore - meaning you get much more muzzle blast with not much more performance.

The 30/06 AI and 280 AI are almost twins in performance, and a better 30 caliber would be a 30-338 or 300 WM. 30/06 AI is underbore IMO, although quite efficient. The 30/06 (AI or not) will provide more-than-enough killing power for North American big game with less kick and muzzle blast than the larger powder capacity big-bore mags.

First let me state I have more wildcats or improves than I do factory.

Loaded to the same pressure the gains in Velocity are small. You see a big jump in the 257 and 280 because factory pressures are low. Most gains seen are from higher pressure. Figure 1% velocity for every 4% increase in powder. Look at the velocities between the 308 and the 30-378. The 30-378 uses 100% more powder than the 308 to get 16% more velocity. While the AI might be a little more efficent there is no way you can add some of the claimed 10-15% velocity increase with only 5-7% case capacity at equal pressures.

While I don't normally have to trim my AI cases I don't trim that many factory either.

I've read you get less thrust but have now way of proving it.

I have mine because they are different and make excellent topics around the hunting campfire.

If you want something unique go for it. If not take the factory round and load it to 63,000-65,000 and be done with it.

In a .220 AI, you definitely will go from trimming virtually every loading to every fourth loading, and pick up 150 fps as well. The 7x57 is another cartridge that will need trimmed almost every firing, so I assume the same with a .257 Roberts since they're the same case design. In a varmint cartridge cutting back on the trimming is a big deal for me, in the others it's not that important. The .22-250 has just as much taper or more than the .220, so I'd expect it to work out much the same way.

I'd do the AI. It does reduce trimming which im not fond of. velocity gains like everybody says are piddly but it looks cool. Fireforming isnt a big concern being as you ony have to do it once per batch of brass. i formed mine with cornmeal and pistol powder. it was OK but i dont know that the bullet and mild load method isnt better. One problem i had with my gun was going from a 30-06 case to a 6mm-06 AI i had feeding problems in the gun. The rails on my CZ 550 are too tight to work properly. Another problem i had was with my sinclair neck turner. i had to buy the 40 degree cutter because the 28 degree cutter hits the shoulder before it would turn the full length of the neck on the AI case.

Thanks for the info, I guess I was on the right track. There are some pros and cons. I just like the way they look.....

Nothin but a headache, you have to load it once to fireform the case and then you get to shoot the ackley version the second go round so while your waisting your time fireformin you could be doin the real thing, also it costs more too, but i guess as long as it floats your boat and you like spendin money for nothin then I say go for it because there are really no big advantages anywhere but in your pocket book.

Quite a few years ago, I got myself a .280 AI - mostly because it was the "hottest" thing on the market at the time, it was supposed to give me 7mm Rem Mag ballistics in a .22" barrel, all at less recoil and muzzle blast... And, I guess, because I was young and gullible at the time...

Since then, I have shot that rifle a lot. Now that I'm a lot older, and although probably just as gullible, I doubt I would have bothered with the AI, if I had to do it all over.

I found, that if I wanted 7mm Rem Mag ballistics, I needed a bigger case, otherwise I'd forever be riding the pressure curve. It was quite a bit of hassle having to fireform cases. Having fireformed, I found cases would often have workhardened sufficiently, that it was necessary to anneal to ensure consistent neck tension. I can be pretty sure, the rifle has almost zero resale value, being chambered for a wildcat caliber. The extra 100 fps the AI chamber might have given me compared to the regular .280 Rem were nice, but probably pretty meaningless in terms of real field performance.

So all in all, probably the only real advantage going with the AI version gave me, was that I never had to trim my cases in that particular rifle. That was nice, but probably not worth all the hassle.

- mike

If you want one that's reason enough, especially if you are going from the action up & not rechambering. I wanted something a bit more usefull on my M700VS than the .308. So I decided I needed a .260 but then thought why not a .260ai? Same cost to rebarrel, you can use Lee .260 neck dies, so no increase in die costs. Fireforming is a PITA, but I did quite a few while breaking the bbl. in, & sighting the scope. Then every trip to the range I take 3 rds for fouling the bbl. & checking the chronograph, so I'm not really "wasting" any rounds. Cases last forever, minimal to no trimming & not everyone has one. What's not to like?

The AI issue has been discussed on this forum a lot.....those that claim little velocity increases are with the majority of replies.....

I had a .270 AI built just because I kinda like the "oddball" stuff. Like others, the velocity increase was small, around 50-100 fps. The dies are also quite a bit more than the std calibers.

Case life with the 6MM AI will be better thatn the standard 6mm provided you don't start loading up and looking for pressure signs with you AI. AI cartridges "mask" some of the conventional pressure signs because the case does cling to the chamber walls a little longer and bolt thrust is reduced. Get copies of PO Ackley's books- Handbook for Shooters and Reloaders Vol. 1&2 and read what P.O. has to say.