Is it possible to buy an HK416?

Since, for all intents and purposes, it's just a dressed-up gas piston AR, you could buy any gas piston AR and have what amounts to the same thing in a civilian-legal package.

All the HK416 is, is an AR with a G36-type gas piston, essentially. Just get a less expensive gas piston AR, and have a ball. LWRC's M6 would be a good possibility.

The semi-automatic version, the MR556A1, is available to the civilian market. There is also an upper designed to work with standard AR-15 lowers, which is less expensive.

All in all, the MR556A1 doesn't get great reviews. It's pricey ($3,000 to $5,000), difficult to find, and takes proprietary HK magazines. Like most HK products, it is overexpensive and overhyped. While it may be more reliable than standard AR-15 designs, most civilian shooters don't shoot nearly enough in cruddy conditions to notice the difference.

If you have the cash and can find a dealer to track one down, purchasing a MR556A1 is the same as any other AR-15 rifles, barring state laws.

Only if you have a Class 3 FFL.

For police & military sale only. http://www.hk-usa.com/index.asp

Whatever crappy civilian version they make.