I cant help you with the specifics for chambering. However, after looking into the 260AI the gains weren't really worth the effort.

I'm getting an easy 2800FPS out of my standard criterion tube with the 140amax's. Most people with the AI are getting at most 2900 and most it seems around 2850.

In exchange you get a lot more brass work, poorer feeding, and a bigger pain all around.


Just my thoughts.....