I will only add that the military briefly evaluated the new AR-10 in 1956, but years of prior testing of the T44 (aka M14) was basically completed at that point, and it was adopted in May 1957. The Army asked Eugene Stoner to develop a smaller caliber version of the AR-10 which was the AR-15 in 5.56mm, and later adopted in 1964(?) as the M16 - likely due its overall controllability in select fire mode - relative to the M14 which was not especially controllable in full-auto. So the main focus was getting M16s into the hands of troops in Vietnam, and I think the AR10 tooling was sold by ArmaLite to a Dutch company.
The M14 program was canceled in 1963 after only 1.3 million made (it was projected to be up to 5 million made as a 1-for-1 replacement of the US military’s 5 million M1 Garands...long story there).
A few AR10s were made by the Dutch but export sales were very limited and no further development took place from roughly 1960 thru 1990. However in 1990 Reed Knight of Knights Armament hired Eugene Stoner who was the engineering genius and inventor behind both the AR-15 and AR-10 platforms - and together during the 1990s they finally developed the AR-10 and renamed it the Stoner Rifle 25 or SR-25. I have read that Crane was interested in it, and the SOCOM/ Special Forces guys started field testing an early suppressed version of the SR-25 around 1993 in which the original 24” barrel was shortened to 20” and threaded for a suppressor, but tweaks were needed. (Original AR-10 “waffleboard” magazines may have been problematic, etc).
As noted above post, after much testing and refining the rifle, suppressor, and it’s magazines during the 1990s, in 2000 the US Navy at Crane ordered its first 300 SR-25 rifles that became the Mk 11 Mod 0 sniper rifles, and a similar permutation with a flash hider, the M110, was subsequently adopted by the Army and USMC. One of the unique things is the Mk 11 was developed from the get-go as a suppressed weapon system, whereas suppressing the M14 is difficult due to its gas port actuated action, but I digress...
So it was really KAC that resurrected the dormant AR-10 platform by hiring its inventor 30 years ago. Eugene Stoner died in 1997 from cancer, but we can thank his efforts along with Reed Knight during the 1990s for the ultimate development of the Mk 11 Mod 0/1 and M110, etc.
Eugene Stoner was the father of the AR-15 and the M16, and a titan in the world of both military- and civilian-use firearms. This is the forgotten history of how he changed the landscape of American firearms, as well as the world stage, and became the archetypal “self-made American man.”
ammo.com
As for the M14 in the 200Xs, yes it was used by the USMC who had about 400 of the dedicated M14 DMRs made beginning in 2000, and many rack grade M14s were also pulled out of storage by the Army and accurized for DMR use as well in Afghanistan and Iraq, as both showed the need for an accurized rifle with a 600 to 800 meter effective range, which the standard 5.56mm cartridge can’t deliver.
Of course the M16 was also developed as a DMR via the Mk 12 program at Crane (the USMC developed their own SAM-R program), with the key development/ ingredient being the Mk 262 cartridge, which used a heavy for caliber 77 grain low drag bullet to increase range out to 600 or more meters. Afghanistan has a lot of very wide open spaces, as does Iraq...unlike Vietnam.
