Just for the record, the acceptance standard for the M14 was 5 MOA - and many rifles failed to meet this. The problem was traced to ammunition, but this is well documented and even resulted in senate hearings. Details can be found in US Rifle M14 by Stevens. Interestingly, the precision standard was the same for the M1 Garand.
Further, it should be noted that it was the US that pushed the acceptance of the full power 7.62x51 (308) cartridge as NATO standard over the objections of the European members. It was not soldiers complaints but battlefield studies, originally performs by the German army post WWII that led to the concept of the intermediate range cartridge. The rationale was that current rifles were needlessly powerful for normal combat ranges, and an intermediate round would be cheaper to produce and a soldier could carry more. I know of no study that used the desires of the soldiers.
The US was one of the last industrialized nations to adopt the concept of the intermediate round, and this was probably due more to the departure of Rene Studler as head of ordnance than any other factor. He worked tirelessly to kill off support for the assault rifle concept, continuing to support the notion that infantry rifles needed to be effective out to 1000 yard in spite of all the studies that had shown that to not be the case.
The two seminal publication in the US that led to the adoption of the assault rifle in the US are Hitchman's Operational Requirements for an Infantry Hand Weapon and the Hall's An effectiveness study of the infantry rifle. Both were published in the 1950s and while forward thinkers used this to promote the SPIW as the next generation of infantry weapon, it was basically ignored by the insiders at ordnance.
For those unfamiliar with either work, the Hitchman study basically confirmed what the Germs had found in the interwar years - that virtually all smallarms fire occurs at 500 yards or less and effectiveness drop to virtually zero at his range, that 70% of all smallarms fire is at 100 yards or less, and that volumes of fire were more effective than aimed fire in the confusion of combat. The Hall study postulated that a small caliber bullet driven at sufficient velocity would have the approximate lethality of a larger caliber round at combat distances.
The upshot of all this was the adoption of the M14 to satisfy ordnance, but to pursue the SPIW as the long term replacement rifle for US forces. Almost immediately, ordnance started to sabotage the SPIW project by introducing requirements not called for or seen as necessary by the Hitchman study, but fitting in with the conservative, target shooter mindset of Ordnance.
Long range effectiveness was not necessary according to Hitchman, but ordnance wanted a rifle that could be effective out to 800-1000 yards. Burst fire increased the potential for a hit, and slight dispersion was advantageous, but ordnance insisted upon single round accuracy.
The SPIW program fell farther and farther behind thanks to immature technology and conflicting requirements. Meanwhile, the M14 was proving to be nothing more than a product improved Garand, and the Manufacturers were having problems producing the rifle at the estimated cost and required quality. The idea that modified Garand tool could be used to save money proved utterly false.
The M14 problems weren't resolved until TRW took over production, building a new manufacturing facility from scratch. By that time, the M16 was already in the pipe as an interim rifle until the SPIW was ready and production of the m14 ceased just as things were finally sorted out.
The M16 itself was never seen as a permanent solution. It was never subjected to acceptance trials the way previous rifles were, and was adopted through the back door thanks to Colt's sales people pitching the rifle to SAC chief Curtis Lemay, who was something of a gunguy and needed a new high tech rifle to replace the M1 carbines the Air Force was using. SAC was all about high tech, and when the rifle was presented to Lemay at a picnic - which included some watermelon shooting - Lemay was sold. From their the rifle gradually crept into military service. It was seen as a perfect rifle for smaller Vietnamese allies, and gradually the 'interim' rifle became standard and the SPIW project shriveled up and died.
The M16 series - an interim weapon - is now the longest serving rifle in the US, probably a testament more to the conservative nature of the military and Colt's understanding of how to work the procurement process than anything else.
The whole M14/SPIW/M16 debacle also led to the dismantling of the US arsenals and putting the whole contracting of small arms into the hands of private companies - for good or ill.
