Not sure where you're getting this. If you take advantage of the extra case volume, the AI will run equal or greater pressure to generate the modest increase in velocity, and barrel life will either be the same or less. There is no free lunch. Not taking advantage of the extra case volume and using an AI to run identical performance loads as in a straight .223 Rem, except with very modest gains in pressure and barrel life is not worth the effort, IMO. The real advantage of the AI is when you're using a specific bullet weight/barrel length combo in .223 Rem and you just can't quite hit the next node, the small increase in performance with the .223 AI might allow you to reach it.
The downside to using an AI with very heavy bullets (80 to 90 gr range) is that it is quite easy to kill the primer pockets even with standard .223 Rem case running these bullets and stout loads. The primer pocket is not strengthened in any way by the AI brass modification, so if anything, the potential for poor brass life becomes even worse. You can certainly adjust your load to minimize this issue, but what is the real point of taming down a load that you just switched over to an AI cartridge in order to make possible? Of all the cartridges that have been AI'd, the .223 Rem to me makes the least sense. The gains are really very small in relation to the parental cartridge. I've run 90 VLDs out of a straight .223 Rem F-TR with a 30" barrel for years at ~2850 fps out to 1000 yd. If I ever need anything more than that, I have a .308 Win with 200s.
