While only FN and Colt supply AR-style rifles to the U.S. military, plenty of American gun manufacturers supply arms to other militaries worldwide. Czech and Georgian units are known to use Bushmaster carbines, a large stockpile of Georgian Bushmasters was captured during the 2008 war with Russia. However, in recent years, Sig Sauer, Inc. has stepped into the market, competing with Colt, Bushmaster, and smaller companies like Rock River Arms. Sig Sauer, Inc. makes a variety of AR-15 style rifles, including the gas operated SIG516. But in direct competition with the various Colt M4s is the Sig Sauer M400, their own take on the direct gas AR-15 rifle.The original M400 is a fairly standard AR-15. The primary difference it has versus a Colt M4 is a slightly altered lower receiver, which has built-in sling swivels at the rear of the lower receiver and slightly beefier/flat fencing for the magazine catch. Original export M400s lack a free float barrel and feature a standard “A” frame front sight and a carbine-length gas system. Ironically, most police and military users of the M400 are rarely seen using these built-in sling swivels. Internally, the M400 has a special support pin in the locking lug recesses that keeps the extractor pressed against the cartridge to prevent a blowout in the event of a squib load.The M400 was made notorious during the battle of Mosul. Iraqi Special Operations Forces ordered a large number of the rifle, and many photos of ISOF members during the battle show them with the M400, though other AR-style rifles are present.