All About Guns

The Origin of the Species: The Model 602 M16 by WILL DABBS

Today’s latest M4A1 Carbine is the end result of more than half a century of martial evolution. From morphology to metallurgy, the Carbines our boys and girls carry into combat today bear little semblance to those primitive M16 rifles their grandfathers wielded in the early stages of the Vietnam War. While forearm rails and electronic optics are de rigueur these days, it can be a fascinating exercise to look backward and see where it all came from.

In the Beginning…

The origin story is foundational dogma for gun nerds like us. George Sullivan incorporated the ArmaLite Corporation in 1954 as a tiny little subsidiary of the Fairchild Engine and Airplane Corporation. Operating out of a modest machine shop in Hollywood, California, Sullivan envisioned ArmaLite as a think tank to explore cutting-edge concepts in small arms. Their first serious effort was a small takedown survival rifle intended for use by downed military aircrew.
While out test firing this prototype rifle on a local firing range Sullivan bumped into Gene Stoner. A World War 2 Marine veteran, Stoner had a vision to incorporate aviation technology into the field of small arms. A friendship was born and Sullivan hired Stoner as his chief design engineer. As of 1956, ArmaLite had a grand total of nine employees.
The resulting guns were indeed radical. Employing aircraft aluminum receivers and phenolic synthetic furniture, these early ArmaLite rifles were justifiably compared to the science fiction weapons of the day. Employing a gas-operated, magazine-fed action and inline architecture to help manage recoil, these earliest black rifles were shadows of the great things that were to come.

This modern retro replica of a Model 602 M16 is almost but not quite perfect. It is amazing how lightweight these old guns were before we started hanging so much stuff off of them.

The AR10 fired 7.62x51mm ammunition and was exceptionally lightweight. That earliest prototype weighed a mere 6.86 pounds empty. This radical rifle was briefly pitted against the T44 and T48 in the contest to select the US military’s new Infantry arm. The T44 became the M14, and the T48 was an Americanized version of the FN FAL. While the AR10 fizzled in 1957, events were unfolding in both Washington DC and Southeast Asia that were destined to tie the ArmaLite design to the United States Military for generations to come.
The AR10 was built under license in the Netherlands for a time and saw action with Portuguese Special Forces in Africa. Eventually, the basic AR10 action was scaled down to accept a .223 cartridge for what was called the CONARC trials. CONARC stood for Continental Army Command, and these tests sought to select a new lightweight combat rifle that would be both easy to carry and controllable on fully automatic. In 1958 ArmaLite submitted ten rifles and one hundred 25-round magazines for the tests. Though the compact bantamweight weapons performed well, internecine political squabbles conspired to torpedo the lithe little gun. Frustrated with the lack of progress, ArmaLite sold the rights to the AR10 and AR15 off to Colt.
A lot of fairly tedious political stuff happened at this point that we will ignore in the interest of brevity. Ultimately the new type-classified M16 made its way to Vietnam for troop trials. Those earliest M16’s fell into several broad developmental categories based upon various arcane technical details. With the recent interest in everything retro, a cottage industry has arisen around sourcing parts to build modern-day replicas of these exceptionally rare guns. The rifle we will dissect today is most closely described as a semi-auto replica of a Model 602 M16. Some of the details are not quite perfect, but it is awfully close.

Early Morphology

From nose to butt our replica Model 602 M16 sports a three-prong duckbill flash suppressor. There were two major variants, and the one on my rifle is the first. Early barrels sported a 1-in-12-inch twist rate and were not chrome lined. Front sights had a round cross-section and could technically be adjusted for elevation using the nose of a bullet. There were tiny variations in gas block markings, but I cannot dredge up enough enthusiasm to care.

This first model duckbill flash suppressor sports open prongs that were notorious for catching on stuff in the jungle.

The triangular synthetic handguards were initially painted green before being ultimately left black. They came in dedicated left and right-hand versions and included pressed steel heat shields. The furniture on my rifle is original early Colt and was painstakingly sourced. Those early slip rings were straight-walled and fairly difficult to manage.

These original early Colt triangular handguards include steel heat shields and are secured via a straight slip ring.

Early upper receivers lacked a forward assist device and included a simple flip-adjustable peep sight. This sight was adjustable for windage via a bullet tip. An aluminum carrying handle was formed as an integral part of the upper receiver assembly.

The original slab side M16 receivers lacked a raised fence around the magazine release catch. The forward pushpin was also not captive.

The lower receiver was flat on both sides, lacking the elevated fencing around the magazine release with which we are familiar today. The forward pivot pin included a detent in the pin itself but was not positively retained, so it could be easily lost. The charging handle had a fairly small triangular gripping surface. The bolt and bolt carrier were hard chrome plated, and the firing pin retaining pin was a specifically manufactured component rather than a standard cotter pin.

Very early charging handles had a small-ish triangular serrated gripping surface. Later versions are much easier to use.

The buttstock was solid and lacked a trap for cleaning gear. The earliest rear sling swivels pivoted, while later versions were rigid. The earliest Edgewater buffers included a series of washers not found on subsequent designs.

The first M16 buttstocks lacked a trap compartment for cleaning supplies and sported a freely mobile rear sling swivel.

While those earliest M16 magazines were straight-walled and carried twenty-five rounds, the first general-issue mags were imbued with a waffle pattern and took twenty. Early AR10 magazines sported a similar design. Followers were short and prone to tilt.

The singular best improvement to the M16 over the years has been in its magazine. From left to right, an early 1950’s-era 20-round AR10 waffle mag, a later AR15 20-round waffle magazine, a Vietnam-era Colt 20-round M16 box, and an Information Age 30-round P-Mag.

Trigger Time on the 602

It is amazing how lightweight these old rifles were before we started hanging stuff all over them. This primitive M16 clone weighs just a hair over what an M1 Carbine might while throwing a much more effective round. Recoil is mild, and follow up shots are fast. While my retro clone is semiauto only, I have run a few zillion rounds through similar GI full auto M16A1 rifles back when I was young, bulletproof, and immortal. Those guns do not well suffer sloth when the Happy Switch is set to the Hallelujah position. However, if you lean into the rifle, use proper technique, and keep your bursts to a reasonable length the gun remains a formidable close combat tool.

The earliest model M16 rifles used in Vietnam sported three-pronged open flash suppressors and lacked a forward assist device.

The simple flip-adjustable peep sights seem crude compared to modern electronic optics, but they were light years ahead of most World War 2 designs. Adjusting the sights while zeroing the rifle was a chore without a dedicated aftermarket sight adjustment tool, but I kept one in my LBE (Load Bearing Equipment) that I was always willing to share. The general layout of the M16 interfaces unnaturally well with the human form. While much about the gun has changed, the basic switchology remains the same.

Men of the 1st Brigade, 101st Airborne Division, fire from old Viet Cong trenches

Back when I had good eyes I could consistently shoot expert out to nearly half a kilometer with a rifle very similar to this one. Running a few rounds through this nifty little gun brings back lots of memories. The distinctive twang sound as the buffer cycles millimeters from your face is like the voice of an old friend.

So Why Did They Change Everything?

The three-prong open-ended flash suppressor was great for prying open the wire around ammo crates, but it was notorious for catching on vines and such when moving through thick brush. If you’ve never had the pleasure of humping the boonies with a weapon for real you develop a oneness with the environment that really has no civilian parallel. I once saw a young man unwittingly carry a dead lizard that was nearly twelve inches long around in his BDU shirt for half a day. It was simply that he was so filthy he did not realize the unfortunate creature had crawled down his shirt and then been crushed to death by his rucksack. That poor guy looked like he was having a seizure when first he realized he had been walking around all night with a foot-long dead reptile curled up in his armpit. I don’t know about anybody else, but I first joined the Army for the glamor.

Early M16 rifles were by all accounts very successful in the hands of Special Forces and indigenous troops in Vietnam. Subsequent changes to ammunition propellant and the lack of proper maintenance gear and training precipitated a disaster.

Those thin raw steel barrels have been beefed up, chrome-lined, and had their rate of twist tightened. The many-splendored impact this has had on lethality would fill a textbook. Bullet design has evolved substantially since then as well, but nobody will ever be happy with it all.
The triangular handguards were slippery when wet and prone to breakage. The newer round versions we used before everybody bought forearm rails were tougher and interchangeable, so it was easier on the supply guys. The straight slip ring grew a taper, so it was easier to manage.

US Army Special Forces serving in Vietnam were some of the first American troops to use the M16 operationally. Note the three-pronged flash suppressor and slab-sided upper receiver.

Modern M4 rifles traded their carrying handles for Picatinny rails, so our current crop of kids serving downrange can see farther and shoot faster than old geezers like me ever could. Modern iron sights are much easier to adjust without tools, though I have not personally ever seen anybody use them as intended at long ranges. Today’s bolt carriers are not so shiny as was once the case, and stepped-up extractor springs are hugely better than they used to be. Today’s charging handles are much grippier than those earlier sorts, and the rigid rear sling swivel always looked to me like it would carve somebody’s face off if you used it for a proper butt stroke.

Once the M16 rifle had matured somewhat and was subjected to proper maintenance it became a reliable and effective combat tool.

I have had an errant tree branch center punch my mag release while crawling through brush and drop my magazine, but the raised fencing makes that unfortunate event much less likely.
Anything that comes off the rifle is something you can lose. Today’s captive takedown pins are an enormous improvement. The 1911 pistol is indeed an inspired contraption. However, I once saw a young stud launch his recoil spring plunger into the stratosphere while stripping the weapon in the field. That thing is still likely out in space somewhere orbiting the sun.

The lack of cleaning gear and basic rifle maintenance training resulted in poor performance for the M16 early in its operational life.

90% of the many stoppages I encountered with those old M16A1 rifles stemmed from that repugnant stubby magazine follower. Those early magazines were notorious for allowing the round stack to tilt and produce a bolt over base stoppage. Compared to those old boxes a P-Mag is an incalculable improvement.


This particular rifle has an interesting story. The gentleman who built it acquired the various components from a dozen different sources over months of searching. The end result is a simply superb semiauto rendition of an early Model 602 M16. However, this guy had the profound misfortune to live in the People’s Republic of California. The laws changed, and he had to sell the rifle to somebody living in the Free States. I felt like I was taking receipt of an abandoned child.

Today’s modern M4A1 Carbine stemmed from the original 1956-era AR10. This gun was built up from an imported Dutch parts kit on a domestically produced receiver.

Today’s state-of-the-art M4A1 sprouts lights, lasers, and holographic optical sights unimaginable a generation ago. The beating heart is the same simple direct gas impingement operating system that you either love or hate, but most everything else about the gun is fresh, new, and different. The changes we have seen in the M16 platform over the past half century are well-reasoned and effective. Until the BlasTech E11 Stormtooper blaster becomes widely available the venerable M4 will still keep soldiering along. More than most any other contemporary mechanical contrivance, in the M4 we see the most overt evidence of martial evolution in action.

The 1960’s-era M16 rifle has come a long way in half a century. While the beating heart is unchanged, the external morphology is all but unrecognizable.

Technical Specifications

Model 602 M16
Caliber                  5.56x45mm
Action                  Direct Gas Impingement
Barrel Length        20 inches
Overall Length      39.5 inches
Weight                  6.37 pounds
Feed System         20-round Detachable Box Magazine
Rate of Fire           700-950 rounds per minute

Performance Specifications

Model 602 M16
Load                               Group Size (inches)        Velocity (feet per second)
American Eagle 55gr FMJ                 1.6                        3091
American Eagle 50gr JHP                  3.6                        3372
HSM 55gr Sierra Blitzking                 1.2                        2976
SIG 60gr HT                                         5.6**                    2605
**These rounds seemed to keyhole. Apparently, the old slow twist barrel was inadequate to stabilize them.
Group size is the best four of five shots measured center to center and fired from a simple rest at 100 meters. Velocity is the average of three shots fired across a Caldwell Ballistic Chronograph oriented ten feet from the muzzle.

These Vietnam-era rifles are on display in the National Firearms Museum. This collection includes a prototype ArmaLite AR10 as well as a pair of early M16 variants.

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