The .308 Winchester( 7.62mm NATO) round is the most widely used round,although the .300 win mag and .338 Lapua have a strong following with the long range military shooters.Rifles built on the Remington 700 action are common,but with law enforcment agencies,alot has to do with their budget.Big budgets could even mean custom rigs where those dept.' s on tighter cash flows may only use factory options.I have even heard of some using confiscated rifles in their tactical units.

Sorry...can' t answer your second question for sure.