As noted in Lysander's posts #29 & 31, there was an obscure "M14 Modified" or "M14 (M)" prototype configuration that was tested as a replacement for the heavy-barreled M15 as a Squad Automatic Rifle (as the Browning BAR replacement). Note: The M15 platform was canceled in late 1959:
"COMFIRMATORY TEST OF PRODUCTION MODEL RIFLE, 7.62MM, M14," 23 October 1959, (USAIB).
"...a. Evaluation and service tests of a number of different type rifles including the Rifles, 7.62mm, T44E4, and T44E5 were conducted by this Board in 1956 (ref 2 and 3, Annex D). These tests revealed that in general the T44 rifle system was more suitable for Army use than the other types tested. In May 1957 the T44E4 and T44E5 rifles were adopted by DA as the standard, rifle and automatic rifle respectively. The T44 was standardized as the M14 and the T44E5 was standardized as the M15 rifle. The test rifle is the production model M14 rifle modified to correct previously reported deficiencies. In 1959 this Board determined that the M14 rifle with a hinged butt plate, slotted handguard, and detachable bipod was suitable as an automatic rifle and recommended that it replace the M15 rifle (ref 6, Annex D).
“REPORT OF COMPARATIVE EVALUATION OF BIPODS FOR THE M14 RIFLE IN THE AUTOMATIC RIFLE ROLE,” 29 October 1959, (USAIB). Abstract- compares the Type II bipod (bayonet lug mounted, the best candidate from the first report) with the Type III bipod (gas cylinder mounted). It also tests the suitability of the plastic handguards and hinged buttplate, both modified to correct deficiencies identified in SERVICE TEST OF RIFLE, 7.62MM, M14 MODIFIED FOR THE BAR ROLE. The handguard, now stiffened by longitudinal and radial ribs, the aluminum buttplate with steel shoulder support flap, and the Type III bipod are all approved as suitable for Army use."
As far as I can tell from those test reports circa summer/autumn of 1959, these six "M14 Modified" test rifles were the very first rifles that used the initial aluminum+steel production hinged buttplate and a ventilated fiberglass handguard
. (Those two items would later be incorporated into standard M14 rifles during the mid-to-late 1960 era, but I thought I'd do a replica of that rifle given the early M2 bipod that I recently acquired). Interesting diagram in Frank Iannamco's book; The U.S. M14 Rifle
(2018), page 128. (My guess this is diagram is from late 1959 or early 1960):
So, for the heck of it, I took my replica of an SA NM M14 and mocked-it up as one of the six "M14 (modified)" or 'M14 modified for BAR role" rifles tested back in 1959. Per Lysander posts # 29 & 31, they consisted of an M14 with the prototype 'hinged' or 'flapper' buttplate, the newly designed M2 bipod (without a front sling swivel), the prototype ventilated handguard, and of course a selector switch. Top is my replica of an 'M14 modified' and bottom is my replica of the T44E4, which is what the standard infantry M14s looked like circa 1959-1960 (M1 buttplate; wooden handguard, no bipod - and selector locks are already seen on some of the archival pictures, so by 1960 the standard infantry rifle was presumably to be configured as a semi-automatic rifle - and the 'M14 modified' version would be the select-fire, squad automatic version with the selector switch, along with the M2 bipod).
The motivation for doing this quick mock-up was the early M2 bipod that I found on this forum. This design was apparently tested in the summer of 1959, with the drawing finalized in the autumn of that year, and entering mass production in either late 1959 and/or 1960. Unlike the two prototype M15 bipods that connected to the special M15 flash hider, the so-called "type 3" bipod connected to the standard M14 gas cylinder. (Later M2 bipod designed circa 1963 has the front sling swivel for the special M14A1 sling, and a slightly improved 'claw' attachment mechanism).
...Well, as noted in Frank Iannamico's book, around 1960-62', it had been determined that the "M14 Modified for the BAR role" was simply not accurate or controllable in full-auto, and thus it was not issued. However, the desire remained for a more controllable squad automatic rifle based on the M14, which subsequently led to the development circa 1962-63 of a new 'straight-back' stock with a pistol grip, and a forend grip (aka, M14E2 stock); revised bipod, special sling, and a muzzle stabilizer to control muzzle rise.
Anyhow, here's one more pic of what was supposed to be the Squad Automatic weapon circa 1960 as a replacement for the Browning BAR (an older 30-06 weapon). However, only a few prototypes were tested and the US Army decided that a new stock was needed to control the M14 in full-auto mode (as outlined in this thread re the history of the M14E2/M14A1 platform).
Just my random contribution for today of an obscure M14 variant that had a very short life.