The Complete Guide to Colt M-16 Models: Part III

By Dan Shea

Colt 639 “XM177E2”. 11.5” barrel, flash suppressor slots on the moderator, collapsible telescoping buttstock, forward assist. This is the ultimate end of the CAR-15 program. The XM177E2 was issued to the MAC-SOG teams in late 1967, early 1968.

In this, the third part of our Colt Models ID Series, we jump over several models that were minor variations or numbers that were never used. We start with the famous Model 639, the last of the CAR-15 series. The first two versions were the XM177 (Air force) and XM177E1 (Army). We end this part with the M16A1 factory sniper rifles and the closed gas system first model 703. Then, per reader request, we cover the basic grenade launchers that Colt implemented. This series just keeps growing, and we are now up to five parts. In Part IV we cover the M16A2 models. Part V covers the unusual variants that Colt manufactured- the CMG series, the Imp, as well as the ACR. SAR is planning to continue this ID format into the various models of semi-automatics manufactured by Colt, as well as the AR variants made by other manufacturers. This is at the request of our loyal readers, who want a guide to go back to for the semi-automatics as well. Remember that this ID Guide is a work in progress, as we gather information we will add it.

Colt 645. Heavy barrel, forward assist, 1” longer buttstock, 3 shot burst control. This is the first prototype of the M16A2 rifle. Model 645 had a custom made rear sight that allowed both windage and elevation adjustment with a dial, and there was a brass deflector added behind the ejection port. The barrel is a true heavy barrel, with a full contour. Full length round handguards are added to this model for the first time.

Colt 649. 11.5” barrel, no forward assist, telescoping buttstock, flash suppressor slots on the moderator. The sliding buttstock has two positions, and is rubber coated. The Model 649 is the commercial, non-government version of the Model 639, made without a forward assist.

Colt 651. 14.5” barrel, forward assist, fixed buttstock. The Model 651 was a carbine version of the M16A1 rifle. 14.5” barrel length is an optimum length for the M16 system, and provided a shorter overall length that translated into better maneuverability for the operator.

*Colt 652. 14.5” barrel, no forward assist, fixed buttstock. The Model 652 was the Air Force version of the 651, lacking a forward assist.*

Colt 653. 14.5” barrel, forward assist, telescoping two position buttstock. Bringing the overall length of the new carbine design down with a sliding buttock was the intention here, in this “Father of the M4”.

Colt 655 “Sniper”. Heavy barrel, fixed stock, forward assist. The first M16A1 sniper variant is referred to as the “High profile” as the Leatherwood 3 x 9 scope is mounted on the standard carrying handle.

Colt 656 “Sniper”. Heavy barrel, fixed stock, forward assist, modified gas block with hooded front sight. The second version of the M16A1 sniper was modified for the job. It had a new upper receiver without a carrying handle, which lowered the Leatherwood scope considerably.

Colt 703 “M16A2”. 20” barrel, fixed buttstock, forward assist, 4 position 3 shot burst. Buttstock is slotted for a sling. The Model 703’s had a closed type gas system, driving a piston to the bolt carrier. This system was an attempt to replace the original Stoner design, but it was not adopted.

*The first grenade launcher system for the AR-15 series was a spring steel collar that helped in utilizing standard muzzle launched rifle grenades.*

*Colt XM-148. 10” barrel 3 lbs overall weight. The XM-148 has a shortened front pistol grip that facilitates opening the breech.*

A) The trigger can rotate up on the side of the magazine well for carrying.

B) The cocking lever must be retracted to cock the XM-148 The trigger system was a maintenance problem, and contributed to the ending of the XM148 program in Vietnam.

Colt’s 40mm grenade launcher series started with the CGL-4 which was a prototype run. After testing, the CGL-4 became the XM-148 with some improvements.

Releasing the barrel to open the chamber was difficult, and caused problems in the field.

Colt’s first “Quadrant” type sight was fairly fragile, and was easily knocked out of alignment- at a range of 400 yards, this made a lot of difference.