This is actually a straight case .50 cal round that was developed by the Leitner-Wise company as a concept in 1994 in the same vein as other larger bored, AR platform type cartridges to overcome the lack of knock-down power of the standard 5,56 NATO round. It was originally loosely based on the 50 Action Express handgun round that LW modified and in an attempt at making the .499 LWR more reliable, a short stroke gas piston system was developed but that was not enough to produce a reliable large bore rifle, as the large bore straight walled .499 cartridge was not optimal for reliable feeding or extraction in the M16 receiver. It suffered from further early design problems and the project was shelved until around 1998 when it was decided to fully develop the system for the commercial market as well. The first versions were presented at the 2000 SHOT Show, where it gained and interest and a development contract from the US Coast Guard but the contract were terminated in early 2004 because of reliability – not of the LW Rifle – but the conversion of parts with existing 5,56 rifles. The company went through a restructuring process and in 2006 was changed to the LWRC (Land Warfare Resources Company). More info HERE