Produced around 1983. Here’s part of my old rec.guns faq on the SP1.
The Colt AR-15 model SP1 (cat.#R-6000) was in production from
1963-1985. I have noted many slight changes made to this model
during its production run. The following information is from notes
I have made on the AR-15's I have owned.
Rifle Ser#: 14XX
Flash suppressor: type 2, open 3 pronged
Barrel: non chrome-plated, markings: "M," "VP" inside a
1 in 12", barrel twist
Sling swivels: moveable, plastic coated
Front sight base: machined and polished smooth, bayonet lug
Handguard: triangular, black in color
Delta ring: round
Upper receiver: no forward assist, markings: "VP" inside a
Lower receiver: cross drilled for roll pin to retain buffer tube
Lower receiver markings: right side "+"
left side: AR-15 COLT'S PATENT FIREARMS MFG.CO.
CAL.223 HARTFORD, CONN.
MODEL SP1 U.S.A.
Bolt: chrome-plated, marked "MP"
Bolt carrier: not notched for forward assist, 5/8" of rear
bottom carrier milled away(compared to M-16), no machine
cut on bottom of carrier to expose head of firing pin,
markings: none, finish: parkerized
Firing pin: early, heavy type with large head
Firing pin retainer: machined split pin
Hammer: not notched
Safety lever: hole in center of each side
Buffer tube: anodized green
Buttstock: solid buttcap, no trapdoor, color: black
Buttstock retaining screw: solid, no hole drill through
Rear sling swivel: moveable, black plastic coated
Buffer: early light buffer with "Edgewater ring springs"
Rifle Ser#: 48xx
All features same as # 14xx
Rifle Ser#: 78xx
All features the same as rifle #14XX except as noted.
Barrel: markings: "MP," "s," 12 Upper receiver: markings,
"c" in square, triangle
Lower receiver: markings, SER. changed to SERIAL
Bolt: finish, parkerized
Bolt carrier: 1 1/4" milled away from bottom rear of carrier
Firing pin retainer: cotter pin
Buffer tube: anodized black
Buttstock screw: hole drilled through, to let water out
In 1967 the M-16A1 was adopted. Colt began to add some of
its mods to the AR-15 by 1968. These rifles are in the
10,000-14,000 range. This next rifles was made in 1980, it
has the mods from the M-16A1 that were added to the AR-15
between 1968 and the end of the SP-1 model in 1985.
Rifle Ser.# 122,xxx
Features the same as those on rife #78xx except were noted
Flash suppressor: birdcage
Barrel: chrome bore and chamber, markings, " C MP
CHROME BORE," barrels with just "C" mark are chrome
Front sight base: as forged, not finished as on early guns
Upper receiver: markings, "C," "M," added
Lower receiver: markings, "+" deleted, "SER.SP" replaces
"SER"'and a new company name:
COLTS' FIREARMS DIVISION
Buttstock: trap door in butt
Rear swivel: fixed, uncoated
Buffer: new heavy style
Hammer: notch cut in front top
Bolt carrier: underside milled away to expose firing pin head