Most factory cases that become Ackley Improved's are not hard to form, for many years it has been said that the parent cartridge could be fired in an AI chamber without any problems. I forget the reason why, but it was once explained to me in detail by a gunsmith, and it made perfect sense. I just suffer from CRS sometimes
Some Ackleys are more difficult, because the shoulder is actually moved forward and then blown out to 40 degrees. My 6 Long Dasher is a perfect example of this, but it's not a standard AI by any means.
The guy that built it told me it would out perform the 243 AI. I don't know for sure, but I do know that I can easily get 3300 with 105's and H4350. It fits in a Ruger short action with plenty of room to spare. Probably very similar to the 6-250 AI that Tricky is talking about, and there are alot of good reports on that cartridge too.
260, 7-08, 6.5-284, 6.5X47 Lapua are also good choices IMO. Especially if you are interested in deer at 700 or 800 yds. The 6.5-284 probably holds the candle out of those 4.
In order to get the ballistics of a good 6 or 6.5, you've gotta go really heavy bullets in 30 cal. In fact, ballistically the 6 Long Dasher with 95's at 3300 has less drop and drift at 1000 yds then the 300 WSM
with 180's at 3000 does. It doesn't have the energy or "knock down" power at 1000, but it's ballistically more friendly.
Lots of choices out there nowdays that are better than the 308 IMO.