The early days of the M16 rifle in Vietnam

[Bob Womack]

Dick Culver has two very thorough papers on the saga of the M16 in Vietnam that begin with MacNamarra's cost saving efforts (using up old stores of "dirty" powder, eliminating chrome plating of the chamber). The chrome plated chamber was very important in the cycling of the firearm. Because of the weapon's timing, extraction began while the brass casing was still "obturated" or expanded from the expanding force of the gas discharge. Without the chrome lining, the coefficient of drag imposed by the chamber upon the obturated case was enough to cause a higher than acceptable failure to extract.

Dick also mentioned a derivative failure that occurred in 1968 when the chrome was reintroduced: Once it was discovered that the deletion of the chrome was causing issues, the lining was added back. However, in the production spec with the chrome deleted, the size of the chamber had been properly adjusted downwards to replace the diameter in the prototypes taken up by the prototype's chrome lining. When they reintroduced the chrome lining, it didn't seem right to pitch the already manufactured barrels so they simply chrome lined them -but they didn't re-ream them to make space for the addition of the chrome. As a result, the new chrome-lined barrels went into action and exhibited the same failure to extract, but this time, as it turned out, because the chambers were now out of spec. Talk about a bureaucratic inability to win!

Bob