Page Title

Please click here to visit the "Military Rifle Components Guide" for
additional info and photos of the various components used on this model.

HISTORY / BACKGROUND:
The Colt Model 603 / XM16E1 was the first attempt at providing an improved M-16 for the US Army. The Colt
Model 603 / US Army XM16E1 production ran from early 1964, and transitioned into the Colt Model 603 / US
Army M16A1 in early 1967. It was the first model to incorporate the forward assist feature. This model was
also one of the first to use the "Partial Fence" reinforced lower receiver. This was a "transitional" model and
as such early and late models could have been found with varying component makeups.
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BUTTSTOCK:
STYLE:
Later / Improved Solid Body
Type D

BUTTPLATE:
Solid Rubber

SWIVEL:
Pinned, Metal with
Plastic Covering

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BUFFER GROUP:
BUFFER:
"Original" Edgewater Design

SPRING:
Standard Rifle Spring

TUBE:
Original Tube,
No wrench flats,
Hole in tube at receiver
end to tighten tube

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LOWER RECEIVER:
STYLE:
"Partial Fence"

MARKINGS:
Colt Logo
COLT AR-15
PROPERTY
OF U.S. GOVT.
XM 16 E1
CAL. 5.56 MM.
Serial XXXXXX

SELECTOR:
"Later"

TAKEDOWN / PIVOT PINS:
"Later" Pins

BOLT CATCH/RELEASE:
"Latter" with Raised/Grooved End

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UPPER RECEIVER:
PROOF MARKS / FORGE CODE:
Colt Proof Marks - Triangle & Square with "C"
Located in front of ejection port
No Forge Code

REAR SIGHT:
Raised Directional Markings on Receiver

EJECTION PORT COVER:
"Later" with " Rectangular Plate"
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BOLT GROUP:
CARRIER:
Early - Chrome with
Forward Assist Serrations
Late - Parkerized with
Forward Assist Serrations

BOLT:
Early - Chrome
Late - Parkerized

FIRING PIN:
Improved Light Flat Head

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CHARGING HANDLE:
Current Improved Design

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HANDGUARD SLIP RING:
Flat

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BARREL:
DIAMETER:
0.625" at the Front Sight Base

LENGTH:
20"

TWIST RATE:
1/12

MARKINGS:
Colt Proof Marks
Between FSB Legs

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HANDGUARDS:
Standard Triangular

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FRONT SIGHT BASE:
STYLE:
Early - Cast
Late - Forged, with flash removed

MARKINGS:
Unmarked

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FLASHHIDER:
Early - Improved 3 Prong Flashhider

Late - A1 Birdcage