I fireform my brass by shooting a maximum load of H100V in the standard 243 Win case. With the 95gr Bergers in my 1:8 Shilen x26" I get excellent velocity too. The fireforming loads shoot 1/2MOA and I use them for hunting.
If you are going to the effort of dealing with an ackley chamber and fireforming brass so that it can hold more powder, you really need to use a longer tube to get the full benefit. Otherwise I wouldn't see the point. If concerned about weight, go with a lighter contour, just reduce the firing rate. A 243 AI will burn out a barrel fast if the rate of fire is high.
Perhaps you should state what you hope to gain ? A 6.5 may be more to your liking. FYI, you cannot re-chamber a "regular" 243 Win to an AI without setting back the barrel at least 1 turn on the threads. Otherwise there would be no cartridge interference for the fireforming operation.
Ackley developed the .243 Ackley to help fix some of the issues with the .243 Winchester, and an increase in velocity was not in his mind. The only serious gain in powder capacity is from the 40 degree shoulder, and that's not all that much for the effort. But it still some. The .243's are well known barrel eaters do to their turbulance point and the short neck length (the TP is actually out in the throat). You'll gain roughly .006" in the case diameter at the shoulder at best. 150fps is a realistic gain (if your lucky), but most of the issues will still be there.
A Savage action unlike a Remington is a little longer. I think it's either .150" or .187" longer. A 57mm case will cycle thru it with no problems (I have a mod 12), but will a 6mm case fit in your magazine is another story. A 6mm Remington is a far better round, and a 6mm Ackley is a true long distance call.
What you could do, is to ream the chamber with a 6mm Ackley chamber reamer to headspace off a .243 Ackley gauge. Then either use 6mm brass or necked down 6.5 Sweed brass. Sounds hard to do, but is really very easy to do. With this round you get the best of it all. The desired longer neck length, and a much better TP point (Inside the neck). Barrel will last twice as long as a standard .243 and probably much longer than the .243AI. Ontop of this and the longer neck length is that the longer bullets like the 105 grain Amax will not be seated into the shoulder area. Then you gain even more powder capacity. Best of everything.
If I had a 243 chambered as an ai, how well would factory ammunition shoot out of it? What Improvement would I see in the ai ?
I'm thinking a 24" barrel
The 243 AI is a good way to clean up an old 243 chamber.
It will gain somewhere around 100 ft/sec+ and improve case life.
The "Trick" to good accuracy while shooting standard 243 loads is to use a 243 Head space Gage
and hold it to .0005 to .0000 head space. This will hold the brass in place and minimize case stretch .
When set up this way you can expect 1/2 MOA or better while fire forming factory loads
or full power 243 loads. This also makes fire forming cheep and easy and you don't waist powder
and bullets because you can hunt while fire forming.
The 243 AI can match the 6mm Remington and will fit nicely in a short action.
Here is a picture of a "virgin" and fireformed case for comparison.
I recommend doing the right thing and using a true 243AI "go" gauge to set head space on your barrel. The 243 (in fact 308 Win case family) go gauge is not interchangeable with an Ackley gauge. MansonReamers.com carry all the popular Ackley gauges and can make customs, so no excuse to use the wrong gauge. Given the difference in shoulder angles, it should be obvious why you want to use the right gauge.
You can tell a few things from the pic below. First of all, the height to the base of the neck difference can clearly be recognized. The AI chamber is shorter in this regard, deliberately, so that the base of the cartridge is forced tight against the bolt face. Second, the extra case volume can be recognized. The 243 case does not have a bunch of taper to begin with so it does not benefit from the "Ackleying" as much as others.
Having said all that, I am not having any issues with my fireforming loads, they are just as good as shooting any ammo and given the reduced barrel life, I do not intend to waste my barrel life. My magazine allows the bullets to be seated to 2.9" overall length, which exceeds the throat dimension. But then that is what is advocated by David Tubb, that way the bullet is guaranteed to be jammed securely when it is loaded, as opposed to having a potentially variable jump.
The only gauge I use is the "GO" gauge for the parent cartridge. When the barrel is torqued to the action, my chamber is deep enough that the bolt handle will close half way on the gauge. This allows for variances in brass, from lot to lot and maker to maker, but still allows the cartridge to be 'captured' solidly between the bolt face and the shoulder/neck junction of the chamber. The only times, when chambering an Ackley, that I follow a different procedure is with the new Nosler version of the .280A.I. , where I use both gauges, and the .257A.I. (I've found huge differences in .257 Roberts brass, over the years). My Ackley reamer list; .223AI, .22-250AI, .243AI, 6mmAI, .257AI, 260AI, .280AI (traditional), .280AI (Nolsler), .30-06AI, .338-06AI, 35 WhelenAI. As for barrel life,, think Melonite Black Nitride.
"Shoots real good!": definition; it didn't blow-up in my face. Not everything can be fixed on an internet forum!
I'm really glad you all chime in on this, it's gonna make me think a little more on it. It's hard to believe such a small case would eat barrels up so fast? What kind of barrel life in rounds would a 243 vs a 243ai have? Any experience with that?