"Extensive testing in recent times has shown AI chambers produce AT BEST 1-3% increase in velocity, and much of that is because of pressure increases."
I have seen some of these test, and while true in some cases. They are not in all.
Take the .308 family. That case has less body taper than some/most, and would likely fall into that 1% category. The 06 family, has a little more taper and slightly less shoulder. So there would be more volume gain, with that case.
Where AI's shine, is with cases that have a fair amount of body taper, and less shoulder. And those that were loaded to modest pressures to begin with. So yes most of the velocity is gained through the increase in pressure. But some is gained naturally, by more volume. I gain more than some/most because I shoot single shots, and with that I can seat the bullet out farther increasing case volume also.
As far as pressure goes, I don't have pressure equipment either. Whether it be an AI round or commercial load, I load the same. I start by checking various manuals, and select a starting load. I'll load up till that particular firearm tells me enough is enough. Then out of prudence, I will back of 1/2 to 1 full grain. Should the velocity not be what I expected, I will try another powder. Should the velocity be there, but not accuracy(most important), I willl start over and play with seating depth, and or other load components.
With 30+ years experience, with wildcats and several AI chamberings. My best guess with 8x57 being chambered to AI, I would expect 60-100fps gain (pending of course the firearms likes and dislikes). From a 2-2.5% increase pressure, and the balance from increased volume. Which I have found to be 10-15 fps per grain increase Now those figures come from using the Powley formulas, which I found out are conservative. Basically, velocity gain is 1/2 of the pressure increase. But sometime back, I had spoken with a couple different powder companies regarding the formulas. And they said that velocity gain is proportionate with pressure with most cases, once a certain level of pressure is reached. I don't remember what that was exactly,and really don't matter, as the gun still tells when I have reached max. and the chronograph, tells me my gain.
And it has been mention again, not all bolt guns like AI rounds. Sometimes you can modify the feeding ramp and mag. follower so they do feed reliably. But then it becomes a question, when does the gain out weigh the expense?
One other advantage of the AI's, is that the sharper shoulder does slow case growth some, reducing trimming for length.
Still, AI's aren't always a practical option, I wouldn't goes as far as to call it absurd.
But I still have fun playing around and shooting, with all the load development involved.
It boils down to,,,,It's your money, spend it as you wish!!!
Dave
