BudsGunShop.com - Would this fit my ATI compact.?

This barrel profile looks like a barrel that takes a bushing It has no taper like the bull barrel. Your ATI has a bull barrel profile. If your slide is cut for the bushing (disassemble and look for the cut) you can fit it to the gun.

there is no such thing as a drop in barrel on a 1911 it will at least need a good gunsmith to check the lockup and minor fitting if you ati has a bull barrel it will take machine work and fitting to install this barrel