We are well under way. I found, under my bench, an old Remington 700 barrel, in good condition, chamber for the 222 Remington Mag. I'll set that back and chamber it for the 223. I would chronograph it first in 222 Mag but the only brass I have is some 6x47 Federal Match which I don't want to waste. Besides, the performance of the 222 Mag wasn't part of the question. I don't have any 40 grain bullets (or "boolits" for the phonetically challenged)so I'll have to buy a box since they seem to be the popular number for use in the AI.
So here is how the test will work: I will chamber for the standard 223 and will load with a powder which requires near 100% loading density. I'll gauge pressure by miking the solid head of the case. I think everyone can agree that, once the solid head shows any expansion, it is safe to say the maximum has been reached. In fact, it can be said that the pressure is slightly excessive if primer pockets become loose with repeated reloading. After establishing and chronographing the top load, I will load and fire one case 10 times to measure case stretching. I'll do this with the 40 grain bullets. I will also work up a load of similar pressure using a 52 grain bullet for those who might be interested. I will not work up a heavy bullet load since this barrel won't stablize it anyway.
I will also work up a load using a powder which will not quite reach max pressures even when solidly compressed. This will produce the situation where the AI is most likely to shine.
After this is done, I'll rechamber to 223 AI and do it over again. The barrel will be set back approx 1/4 turn (.016") so the barrel will be that much shorter. This may reduce velocities by as much as .75 (75/100ths)fps.
As I said, this will take some time. I have other rifles to finish and test as well. GD