First off I talk to much and I think the AMAX would be the best choice for his application, It has the best balance of price, killing power and barrier penetration.
Well I like the SMK for my m1a, I have shot the amax out of it and it worked well but not as good as the 175g smk in my rifle. The military issues the 77g smk in the mk262 round for use in DM rifles, the Marines also have a new bullet called a SOST I don't know the details. But keep in mind just because the military uses it does not mean its the best, they have to fallow the Hague governing the laws of war. It says that the bullet should not cause unreasonable suffering. To bad the regular military does not have the same JAG as SOCOM. Their JAG said "whats unreasonable suffering have to do with it when your trying to kill someone" thus you see them using different stuff, stuff hunters use.
I run in a circle of LE and I am amazed everyday that some are allowed to carry guns, not saying your buddy is just keep that in mind.
My wife's department will give her ammo for her off duty gun, at the very least he should for defensive purposes use what ever his department issues to the officers as a duty round for those platforms.