Ron Reiber's pressure-lab experience with the 40-degree shoulders of AI rounds is they result in somewhat erratic pressure/velocity rises as powder charges increase--which is one reason he prefers cartridges with 30-degree shoulders.
I'm certainly not anti-AI (or improved cartridges in general), as I've owned several over the years, and two right now--including my second .280 AI. But there is a lot of ballistic BS thrown around about them, which I'm less than impressed with.
Many manuals show accuracy loads for many cartridges at or near max pressure levels. Based on some evidence, I suspect this has more to do with modern rifle powders than case design, since they're generally designed to burn best at the 60-65,000 PSI maximum average pressure of modern bolt-action cartridges.
