Since the topic is highly controversial at times, here’s a pretty simple description:
MIL-C-70559 is the military specification for the M4, which incorporates Colt’s technical data package (“TDP”). The M4 TDP consists of a series of prints and geometries (dimensions), a system of know-how, operation sheets, quality inspection methods and access to the master list of specifications and standards that comply with the requirements in Colt’s contract with the U.S. military. The TDP outlines the manufacturing process, materials, tolerances, assembly, finishes, proof testing and dimensions needed to manufacture the weapon. The military specifications (“milspecs”) and military standards (“milstds”) into which Colt’s TDP has been incorporated consist of more than two hundred extremely rigorous standards covering inspection, tolerances, targeting, endurance and interchangeability of parts.
Quality-assurance and conformance with milspecs and milstds are maintained by an onsite U.S. government inspector who keeps an office at Colt’s factory and by a number of Colt’s own inspectors. In the last two years, Colt has fired more than 300,000 rounds of ammunition in testing the carbine and has not experienced a single malfunction.
The M4-carbine TDP is proprietary to Colt, and the U.S. government has designated Colt its “sole source” supplier of M4 carbines. Under the M4 Addendum, the U.S. government does not have the right to procure the M4 carbine on a competitive basis.
Under the M4 Addendum, only Colt can manufacture M4 carbines, except in very limited circumstances and subject to a royalty payment to Colt. The M4 Addendum allows other qualified vendors to supply non-critical parts for the M4 carbine, but only if they are using Colt’s TDP. Critical items include the upper and lower receivers, the hand guard, barrels and other components of the M4 carbine.
In 1999 FN Manufacturing, Inc. (“FNMI”), a small-arms manufacturer that supplies M16 rifles to the U.S. government, challenged the government’s decision to proceed with a sole-source procurement of M4 carbines from Colt. On August 9, 1999 the U.S. Court of Federal Claims upheld the legality of the M4 Addendum, and FNMI’s challenge was dismissed.