Lower receivers, receiver extensions (buffer tubes), buffers (recoil spring guide), springs, bolt catches, pivot/takedown pins, fire control group (FCG) parts etc.
Album by willyp. Photos by willyp. 1 - 19 of 19 Total. 12185 Visits.
"Slabside" 1st production lower First type production "M16" lower, mfg 1959-1963 used on the 601 & 602, known as "slabside" due to it being completely flat on the right side in the mag well area, this lower used a different type pivot pin than later versions that had a small ball bearing at the end of the pin that "snapped" into the counterbore on the left side of the uppers pivot pin lug. This type pin had a problem in the field as it came out fairly easily & could be lost in the field. Also note the hole at rear where the receiver extension (buffer tube) screwed in, early type tubes were screwed in then this hole was drilled thru the lower & the tube threads & a 3/32 roll pin inserted to lock the tube to the lower. The lower shown is a NoDakSpud semi 601 replica & is an EXCELLENT product as is all their M16 series replica semi lowers.
Civilian Colt SP1 model lower Compare this lower to the 601 type, it's cosmetically similiar, it's a "slabside", but instead of a front pivot pin it uses a unique double screw to mount the upper & lower, the hole for the pivot pin/screw is also larger in the Civilian model preventing using a military style small pin upper on an SP1 lower w/o the use of an adaptor. Military models did away w/the "slabside" type lower in 1963, the civilian SP1 used this style from 1964 into the early 90's. Note also the lack of the + on the mag well compared to the 601 & the lack of the hole in rear of the lower for the tube roll pin, although very early examples of the SP1 lower did have these features, up to maybe 1965. The example pictured is from an SP1 carbine mfg in the mid 80's.
603/604 "partial fence" lower The 2nd type lower went into production in late 1963, it was used on early 603 & 604 rifles, it added the raised housing on top of the mag well (Partial fence) which contained the spring & detent pin that held the front pivot pin in on these models as opposed to the earlier 601 style. Note there is a small hole in this housing, this hole was used to lubricate/repair the spring/detent, these holes were NOT present on original mfg partial fence lowers but were originally added by military armorers as an aid to repair & maintain the rifles starting in approximately 1966, this hole was not part of original mfg until the early 70's at the earliest. Another of NDS's line of lowers & the presence of this hole is the only thing that is "not period correct" but would have been added during arsenal repair work. Note also the hole for the tube roll pin, all partial fence lowers would have these as this method of securing the tube was used at least until 1967-68.
607 lower (minor variant of previous) The partial fence lower was in production from 1963 into approximately 1967, it was used on the 603, 604, 605, 609, & all other models up to that time. The 607 required a modification to the lower, in the pic note the addition of another hole just below the tube hole at the rear of the lower, the 607 used a "lock tube" under the buffer tube, this additional hole (only found on the 607) was drilled thru the housing for the rear takedown pin spring/detent housing, & thru the 607 lower lock tube, a roll pin was then inserted which locked the lock tube in place & also secured the takedown spring (which had to be shortened) & pin in place. This 607 lower is another NDS XM16E1 lower modified to 607 form by heatNbeat.
Full fence (M16A1) lower The next version of M16 lower was the "full fence" which added an additonal "fence" around the mag button, reportedly to address the mag button being released accidentally in the field by brush, branches etc. This version came into production approximately 1967 & is considered the definitive M16A1 lower, it was also used on late production 604's & carbine variants after 1967. Very early examples of the full fence lower, 1967 possibly into 1968 still had the hole in rear to lock the buffer tube in place but this was done away w/very early in A1 production, the example shown here does not have the tube pin hole.
M16A2 lower The next M16 lower is the A2, the A2 style added reinforcement to the areas of the rear receiver extension (tube) housing & the front pivot pin lugs, compare those areas in this pic to the previous A1 lower & the differences are obvious. The lower shown here is a Colt 6520 lower mfg in the 90's. These reinforced areas will be seen in a bewildering array of variations as Colt apparently phased them in over a period of time, the A2 first entered production in 1984.
Bolt catch variants Left: early, 601 possibly early 602 Center: interim, early XM16E1/604? Right: late/current, 1965/66 to current.
Bolt catch rear Differences in the bolt catch itself (as opposed to cosmetic differences of the button), the later/current type was beefed up to account for failures of the early style & manufacture was simplified: Left: late/current style Center: interim catch Right: early 601
XM16E1 interim bolt release Original 601 type bolt release had a serrated flat at the bottom, the next style (shown here) added a small extension at the bottom but still had the serrations on the angle, the next (& still current) style has no serrations on the angle.
Extended bolt catch This is reportedly an experimental extended bolt catch release mfg by Colt, they were reportedly removed from rifles which had been returned from service in VietNam.
Extended bolt catch side view
Extended bolt catch On the original card as displayed on Mr Ricca's show table
Mag release "buttons" Top: early 601 Center: interim "many circles" Bottom: later/current style Note: the early 601 variant shown here is an exc repro mfg by HeatNbeat of ar15.com
XM16E1 mag button "interim" Early 601/602 used a mag button w/horizontal serrations, replaced w/the semi-circular style, this one is another variant believed to be a very early variant of the semi-circular style, referred to as "many circles".
Pivot & takedown pins Takedown (rear) pins top row Pivot (front) pins bottom row Left: 601 pins, the pivot pin on the 601 had a flat round head, it was held in place by a spring loaded ball bearing in the pin & was easily lost if the upper/lower was seperated, also note the dimple or divot in center of the round takedown pin which appears to have been to assist in manipulating/opening the pin, early military manuals state "use a cartridge point in the recess to open" Center: 2nd style starting w/the XM16E1 "partial" fence lowers, the partial fence was actually a container for a spring & detent which held the front pin in place replacing the spring/ball arrangement on the 601/602's to prevent possible loss of the front pin when seperating the upper/lower, early versions of this pin also had the "dimples". Right: "later" type, starting in the mid-late 60's, same as prvious but the "dimples" were deleted & are still the type currently used.
Pivot-takedown pins left On the extreme left is the front pivot pin for the 601, note the small "ball bearing" which was spring loaded & fit into a countersink on the front left receiver lug.
Selector Levers Left: early style w/"dimples" to assist in servicing Right: later style w/no dimples, approximately mid/late 60's to current.
Selector Levers right side Left: early w/"dimples" could be found on 601 thru 603/604. Right: later no dimple 603/604's from mid/late 60's on. This style selector is also used on the M16A2 & later models but will have a small "line" or tic marking on the round end of the right side as the M16A2 & later rifles have selector markings on both sides of the receiver (which the A1 & earlier do NOT have) to indicate the selector lever position for a left handed shooter.
Grip screws Left: early 601 screw w/hole. Right: All later models screw. The grip screw w/the hole is reported to be the one used on the 601's (& possibly very early 602's) which may have been due to the original AR15 being designed by Armalite which was a Division of Fairchild which was an aircraft manufacturer, screws in aircraft use a hole to "safety wire" them in place & may simply have been an expediant of ordering them thru their normal "aircraft" quality suppliers.
