All, I have been/am currently working on my report for the visit I took to the West Point Museum, which was described here. At the time of my visit, I had never heard of or seen an example of this rifle, but I now understand what it is. The information is found here. I believe this rifle to be just one of ten examples.

My heavily paraphrased version (sources will be cited in my report):

    In 1967, a congressional sub-committee headed by Senator Richard Ichord convened to investigate the problems plaguing AR-15 rifles in Vietnam. At the time it was believed that a gas piston version of the AR-15 might prove to be more reliable. Eugene Stoner had been working on a similar rifle with a short-stroke gas system at ArmaLite since 1963, the AR-18. The first such version of a piston-driven system on an AR-15 type rifle came from Colt and was designated the model 703. The model 703 used an entirely new upper receiver, built around a long-stroke piston, but left the lower receiver intact. In May of 1969, Colt issued a report titled “Colt’s Automatic Rifle Model 703.” The report stated, that it was Colt’s belief the new gas system would demonstrate better performance and superior durability when compared to the standard direct gas impingement system. It is apparent that the designing of the model 703 was a proactive step by Colt to maintain its military contract if the military decided that a piston-driven AR-15 type rifle was necessary.
    Around the same time, Olin Mathieson Chemical Corporation’s Winchester Western Division was awarded contract DAAG25-68-C-0742, with a mandate to create a system to retrofit existing AR-15 upper receivers with a short-stroke gas system. The goal of the contract was to, “improve the combat and operating effectiveness and reliability of the existing M16A1 rifle” by developing such a system. Under the contract, Winchester Western Division procured 25 unmodified M16A1 rifles to determine the functioning characteristics of the rifles. They then designed, developed and tested at least two short-stroke gas piston systems. They were to fabricate 10 short-stroke models for delivery to the government and were given the task of estimating contractor cost for retrofitting M16A1 rifles with the new system.
    Winchester Western Division decided to use a shorter-length gas system than the original “rifle-length” direct impingement gas system. The first reason for doing so was to prevent the need for designing a replacement for the front sight that was already pinned to AR-15 barrels, which would have been costly. Additionally, a longer transfer rod is more flexible and thus more prone to breakage due to handling and usage. The final reason for using a shorter-length gas system is because it was believed that the system required higher pressure to operate reliably and thus, the gas port was placed in a location that yielded higher pressures on the pressure-time curve. The new gas block was pinned to the barrel under the handguard, and the handguards were modified to accommodate it. The bolt carrier was modified with a solid carrier key. A steel insert in the side of the upper receiver was required to overcome the peening of the receiver at the rear corner of the clearance cut for the cam pin. The peening was the result of the cam pin impacting on the cam slot in the bolt carrier, which thus rotated the cam pin into the receiver.

Shown is the way Winchester-Western dealt with the damage from the cam pin cutting into the receiver right behind the cam slot in the upper receiver by using a hardened steel screw.



    The study concluded that the material cost per rifle was $4.16 and the labor costs would be $4.13 per rifle. The value of machinery, tools and gauges required would be $2,064,000 and the contractor start-up costs would be $205,000. Like the Colt Model 703, the retro fit program was considered viable. However, neither system would completely replace the direct impingement system.

The Colt 703:



Winchester Experimental Piston M16A1 SN 799,168 (link to photo album)

Wow! That is really F'ing cool! I've never heard of a "Winchester M16" in any form of literature or media. Now it makes me wonder what a Short-Stroke Winchester Made M16A1 would look like if Winchester started making them. Im sure a good analog for it would be one of those Osprey piston conversions. Man now I want a Winchester marked lower and a piston conversion kit...Really love how they made room for the new piston! JB Weld and a Dremel!

Would have only been the retro-fit kit.

Okay yeah that probably would have been a bit more cost effective.

Click To View Spoiler

With a 1968 contract date, that would be 1st year of production JB Weld.



This looks like it would be really easy to make a clone of. I'm eyeballing an Adam Arms midlength piston kit to butcher now.

Any closer pictures of the gasblock?

That’s really cool.

Thanks for sharing this info!

Exactly what I was thinking, was hoping to find a Mid-Length 20" barrel but couldn't track one down.

I made this about 8 years ago and still love it. This is a rifle length gas system but this is back when a1 kits were $300 and the piston kit was $100

Attached File


Attached File

You always have really cool stuff!

Looks like I should start shopping around for parts.
At least this will be easier than the other replica I'm working on:

That’s how I would go about cloning one of these too. And everything I have is in the linked photo album

Thanks again for documenting this rifle! Hope to see more soon.