Colonial Marine Corps M656P with standard AN/MTTS-13 scope

Named for the experimental Model 656 “Special Low Profile” marksman variant of the M16A1 from the Vietnam War, the M656P is a marksman variant of the M16A5P.

Weapon Designation:Marksman Rifle, 6.2mm, Pulse-Fired, M656P
Type:Marksman Rifle
Place of Origin:United States
In Service:2031-present
Production History:
Manufacturer:Colt Arms Manufacturing
Weight:7.4 lb (3.36 kg)
Length:39.5 in (1,003 mm) (full stock with buttplate extended/collapsible stock extended)
38.5 in (978 mm) (full stock with buttplate retracted)
35.5 in (901 mm) (collapsible stock retracted)
Barrel Length:20 in (508 mm)
Action:Gas-operated direct impingement, electronically ignited cartridges
Rate of Fire:700 rounds/min cyclic
Muzzle Velocity:3,925 ft/s (1,196 m/s) with M685 round
Muzzle Energy:1,984 ft/lbs (2,704 Joules) with M685 round
Effective Range:1,000 m (1,093 yd)
Feed System:30-round detachable box magazine
Sights:4-12x40mm integral scope, back-up iron sights


Immediately after the M16A5P was accepted as the United States military’s standard rifle, a marksman variant was requested. The M656P was developed and accepted for issue in just over a year, coming into service in mid-2031, alongside the M950P, a heavy-barrelled support version of the M16A5P.


The M656 is an M16A5P with two specific modifications to make it more suitable for marksman purposes: a match-grade barrel, and a different upper receiver with an integrated scope mount intended for a higher-powered scope than the M16A5P and M950P are provided with.


The M656P’s barrel is virtually identical to the barrel used on the M16A5P. The primary difference is the rifling itself. Instead of a 1:9 twist rate, the M656P’s barrel has a 1:7 twist rate to properly stabilize the heaver M685 round. The M685 cartridge utilizes an 85-grain fluted boat-tail cartridge which is considered both accurate and effective out to 1,000 meters.


The M656P does away with the traditional raised front sight block and carrying handle with its integrated rear sight and replaces them with a different upper receiver with an integrated scope mount and a rear flip-up iron sight, and a flat gas block with a front flip-up iron sight. The scope used is a Leupold Optics ARCS, or Automatic Range Calculating Sight, designated the AN/TTS-13 (Army-Navy Telescopic Targeting Sight-13). This scope is an improved version of the Leatherwood/Redfield Adjustable Ranging Telescope used on the XM21 sniper rifle in the Vietnam War, and is designed so that zooming in on a target so that it appears in the reticle a certain way will automatically adjust the scope to compensate for range and bullet drop. The scope has 4-16x magnification with a 40mm objective lens. It can be replaced with the Leupold NARCS, or Night Automatic Range Calculating Sight (military designation AN/TTS-14), which uses passive night vision for operations at night time. The NARCS has all the capabilities of the regular ARCS scope, although it is larger and heavier. After Leupold shut down in 2059, the design plans for both scopes were acquired by Colt Arms Manufacturing and production continued under the same names. Both the AN/TTS-13 and AN/TTS-14 have target-recognition components similar to the M336 targeting computer used on the M45/M56 Smartgun family and can exchange targeting information with other marksmen, smartgun operators, and sentry guns in the area.

Additional Accessories

The M656P is capable of using all of the accessories meant for the M16A5P and is issued with an M3A1 clamp-on bipod. This simple bipod is a lightened, strengthened version of the M3 bipod used in the Vietnam War and is mounted by squeezing the legs together and opening the jaws until they slip over the barrel. When not in use, the bipod is stored in a pouch which holds it in the closed position. The M3A1 is also used on the M950P heavy-barrel assault rifle.

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