A few things....
1) The "not developed here bias" myth - The evidence for this myth just isn't there for the US Ordnance Department. The Krag, the M1895 MG, the Benét–Mercié, the M1911, the Vickers M1916 MG, the M1917 MG, and the M1918 BAR were all designed outside the US Arsenals by private firms or individuals, further just about all of the fore-mentioned weapons were competing against other private designs, such as the .45 cal Savage, the .45 cal Luger, the Lewis MG, the FAL and all the various semi-automatics entered in the semi-auto rifle competition that resulted in the M1 Garand. Weapons designed internally to the Ordnance Dept are really the minority.* The reason the Ord Dept initially did not like the AR-15 was they did not feel that the weapon was fully developed, and felt that it would be about 5 to 10 years before it was fully developed (and this turned out to be true, it wouldn't be until 1969 before all the wrinkles in the weapon and ammunition were ironed out). Further, the Light Rifle Program, that yielded the M14 had taken over 12 years to get a new rifle in production, and had cost far more than anticipated, they weren't about to admit, that after all this time and money, they adopted the wrong rifle, especially when they felt they hadn't. Besides, the SPIW was going to be the M14's replacement, when that program was finished.
2) He alludes one of reasons the M16 was frowned upon was the potential loss of jobs at Springfield and Rock Island. One, Rock Island had ceased being a production facility by the time of WW2 and Springfield was never intended to be a volume producer of the M14, they were supposed to cease production after the design was matured and proven to be producible. The only reason they got additional production contracts was because production from the two intended producers, Olin and H&R fell so far behind schedule.
3) Port pressure and Ball propellant. The ball propellant was not old stocks from WW2, Olin's St Mark's facility had been making ball propellant for 7.62mm NATO for years, this was the stuff introduced for M193. As to the port pressure, nobody had even looked at the port pressure for the AR-15/M16 before 1964-5. Nobody had any idea what the optimum port pressure should be or even was with IMR propellant. And further, they (Armalite/Colt, Olin, and Springfield) overlooked some basic principles when they adopted ball propellant as a replacement of the IMR propellant:
The area under the Pressure-Time curve (see the example below) from primer ignition to bullet exit
is the muzzle velocity. With IMR propellant, the peak pressure was anywhere from 52,000 to 60,000 psi, They wanted to reduce the peak pressure, but maintain the muzzle velocity, which means the area under the curve has to remain the same. So, if you push the peak of the curve down, but keep the area under the curve the same, that means the rest of the curve has to go up. That means the port pressure has to increase. This fact was obvious to some of the engineers in the Ord Dept, but ignored by the OSD's TCC.
Incidentally, all of the information I have presented in all of my posts comes from Edward Ezell and R. Blake Stevens' "The Black Rifle", which is very well referenced, and has many excepts from the actual reports from the period, and quotes from interviews with many of the principal figures, and from reading the full reports called out in the book's bibliography, many of which are available through DTIC.
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* What Springfield, and Rock Island mostly did was take designs offered to the Government, test them and if they showed merit, recommended tweaks to refine the design to meet requirements. Which is exactly what they did with the M16.
Originally Posted by lysander
A few things....
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