I was with 1st Battalion 9th Marines from 11/66 through 8/67. From 01/67 till I left we were operational around Dong Ha and in the DMZ area. We were in a lot of operations and I think it was around 04/67 that we got the M16s, and then it started. You could NOT keep it cleaned enough to work in the dust and the climate that was there. There were a whole bunch of things wrong with the rifle.
Here is part of something I wrote a long time ago:
Here’s some comparison statistic figures between the M-16 & M-14:
M-16 M-14
Chamber Pressure-52,000 PSI(a) 50,000 PSI (a) same as .50 M-2 Machine Gun
(PSI = Pounds per square inch)
Cycling Rate=1,000 RPM + 750 RPM
(RPM = Rounds per minute)
Bolt Locking Lugs = 7 3
Chamber Design = Closed, star Open
All weapons, except a very few, have "eight functions' occurring when fired to complete a cycle;
1. Firing
2. Unlocking * (not for M-3A1 Sub-machine gun)
3. Extraction *
4. Ejection * (not for M-79 Grenade launcher)
5. Cocking
6. Feeding
7. Chambering
8. Locking (not for M-3A1)
* = problem functions with the M-16s
Now here is what was finally determined, (much later), as to what the defects / problems were with these early M-16 Rifles.
1. The powder used in the loads for the 5.56mm ammunition was the old style powder, which was a dirty burning powder. It was fine for the 7.62mm ammunition that was used in the M-14 and M-60, because, these weapon's gas systems, (ARE SELF CLEANING), and are isolated from the receiver / chamber-bolt areas. The M-16 has a gas tube that runs from the front sight ramp to the receiver (carrier key) and dumps hot gases & carbon right into the receiver and chamber area when fired. (The receiver / chamber fowled out real fast, and what happens to oil / lubrication when it is heated up? It turns into gunk.). Some one was trying to save money by using the old powder.
2. On full auto fire the cycling rate was 1,000 plus RPM (rounds per minute). The rifle "over revered" (it was NOT designed for that high of a cycle rate), and just like a car engine something is going to give. The buffer was later changed to one with "counter weights" in it to slow the cycle rate down to 600-650 RPM.
3. The chambers and bores of these M-16s were susceptible to corrosion and rust, (the chambers would develop small pits). And with the high chamber pressure, (52,000 PSI), the brass cartridges would expand and "flow" into these pits locking / sealing the spent brass into the chambers.
The extractors would rip the cartridge rim off the case. Or the carrier would not even cycle.
A new chrome lined chamber and barrel was developed and ALL M-16s were thus modified, (later).
Note: The Russians & Chinese have been chrome lining the bores and chambers of their weapons for years. I never saw an SKS or AK fail like these M-16s did.
I won't own a black rifle to this day!