Where can you buy a M4 Carbine?

Answer 1

You won't get an actual mil-spec, select fire, M4 carbine, but instead, what is often known as an "M4gery". Depending on manufacturer, they can vary in a number of ways. Some of the differences commonly seen in the "M4geries" include:

• Lack of M4 feed ramps
• chrome moly barrel, rather than chrome lined
• 16" barrel, rather than 14.5" (if you want a 14.5" inch barrel, you need to either get a permit for an SBR, or else have a 1.5" flash suppressor or muzzle brake permanently pinned in order to make it a legal 16")
• 1 in 9 rifling twist, rather than 1 in 7
• commercial spec extension tube, rather than mil spec (the difference being that the commercial spec extension tube is actually thicker than the mil spec one past the threads)
• Different method of staking the gas key
• Different bolt carrier group (although several companies will offer an upgrade to a mil-spec bolt carrier).
• Flat hammer, rather than the notched hammer used on military rifles
• Semi-auto only, rather than select fire.

Most of these features (minus the select fire) can be ordered with your rifle, usually at an increased cost. Some really aren't that important - the mil spec bolt carrier isn't really a necessity for a semi-auto rifle, and the gas key staking isn't that big a deal, so long as it's secure on the bolt carrier, and the average shooter isn't likely to put enough rounds through the barrel that they'll actually benefit from having a chrome lined barrel.

You can order them from several manufacturer's websites (Colt, Bushmaster, DPMS, Del-Ton, CMMG Inc., Rock River, Double Star, etc.) to have one built to the specs you want, or you can check Gun Broker, Auction Arms, Guns America, Bud's Gun Shop, etc. for online listings. Bear in mind that, on top of the price you pay to buy it, you'll also have to pay shipping, and you'll have to find an FFL licenced dealer to receive it for you, and they'll usually charge you a fee for that.

Answer 2

Very few transferrable ones were made prior to the Firearm Owner's Protection Act of 1986 (the legislation which, among other things, prohibited the continued manufacture of full auto weapons for the civil market). If any of these are up for sale, you'd have to search for ads on shooters' forums, listings on Gunbroker, Auction Arms, Guns America, etc. under the 'Class III' section.

Otherwise, you could try to find a transferrable M16 or lower, and add your own upper receiver and furniture. Again, you'd be looking at the same sources for that.

If you want a civilian semi auto lookalike, you have a number of sources. If you want the 14.5 inch barrel, like the military rifles have, you'll either have to get an NFA tax stamped Short Barreled Rifle (SBR), or a permanently attached flash suppressor of a length which will bring it to the legal 16 inches. CMMG offers a 14.7 inch barrel which comes to the legal 16" with a standard A2 "birdcage" flash suppressor fixed to it.

As for those, any gun shop can order them, or, again, you can get them from websites such as Gun Broker, Auction Arms, manufacturer's websites, etc. Keep in mind that, if you order one online, you'll need an FFL dealer to receive it for you, and there's usually a fee associated with that.