Whats a good website to buy nice rifles and cl three weapons from?

Full autos produced after May 1986 like the HK 416 and ACR are Military and Law Enforcement only. You will not see these for sell out side of they semi-auto variant. There is only 100,000 legally transferable full autos in the U.S. period. Anyhow, check out Impact Guns.com, Gunbroker.com, or autoguns.com. If those three doesn't have what you're looking for, it's probably not for sell...either by owner or the government.