Pictured in Colt sales catalogs as early as 1965, the Colt 3x20 scope was developed by the Realist, Inc., of Menomonee Falls, Wisconsin as a "private label brand" for Colt (Senich, 1994). Marketed by Colt as both a "sporter scope" and as part of the Colt AR15 "Military Weapon System" the Colt 3x20 replaced the Delft 3x25 scopes that Colt had been offering with early model 601 AR15 rifles sold in the early 1960s.
While the scopes appear to have been widely used by the US military during the Vietnam war, the exact means of distribution and acquisition of the scopes is unclear. The USARV (US Army Vietnam) reported receiving 364 of the Colt/Realist scopes in November 1967 for use on M16 rifles in addition to over a thousand other scopes and mounts for trial purposes on M16 and M14 rifles (Blake Stevens & Ezell, 2004). Many more scopes were probably purchased by soldiers privately or by units on a small scale.
Production of the Colt 3x20 scope evetually shifted from Realist to Hakko in Japan. The exact year of this change is unknown, but probably happened in the late 60s or early 70s. The scope would evetually be replaced by the Colt 4x20 scope in Colt's catalog.
The scope mounts via a single locking nut to the AR15's carry handle. The top knob is for elevation and is marked in yards and calibrated for 5.56x45. The right hand knob is for windage. Focus is set by screwing in or out the rear eye piece and its corresponding locking ring.
Four different reticle patterns were used, inverted post, thin crosshairs, duplex, and inverted post with thin crosshairs. There are possibly other patterns not listed here. While it is unclear when and why the reticle patterns changed, the inverted post (a copy of the Delft 3x25 reticle) was probably the first pattern built.
The scope is similar to the ArmaLite 2.75x20 scope in appearnce and function. The most obvious difference being the unique mount used for attaching the ArmaLite scope to the AR18/AR180 rifle family.
The scope has been widely copied and cloned. Collectors should take care when looking to purchase an original scope.
Images
Realist produced scope with box.
Hakko(?) produced scope with box.
Early Realist scopes have the Colt markings left unpainted and do not have the model "3x20" on them. Instead the words "MADE IN U.S.A." are under the Colt name.
Japnese scopes will have the model "3x20" marked under the Colt name. Japanese scopes will have have Japan marked on the bottom rear of the tube body near the eye focus lock ring. Unsure if all Japnese scopes have this marking.
Japanese produced scopes will often have an passed inspection sticker on the bottom.
Comparison of various scopes. The two left most are Realist produced scopes. Note the variations in placement location and font of the Colt name and scope model.
Comparison of various scope markings. Starting from the left: Realist USA, early Japanese, mid Japanese and late Japanese.(?)
Instruction manual from a Realist scope. Note it is nearly identical to the 1982 manual below.
Colt instruction manual from January 1982. Note it appears the same manual was used for both the 3x and 4x model scopes Colt sold.
Magazine add for Colt 3x20 scope. Supposedly from 1969. Note the option to purchase the scope with a carry handle mount, or with more expensive 1in rings.
Reticle pattens: Inverted (Realist), Thin Crosshairs (Realist), Duplex, Inverted post with thin crosshairs
On XM16E1 and M16A1 rifles during the Vietnam war.
On XM117 carbines during the Vietnam war.
Seen with members of the Baltimore SWAT on the night of September 15, 1976.
Seen mounted on short CAR15 pattern rifles.
References
Blake Stevens, R & Ezell, E. (2004). The Black Rifle: M16 retrospective. Collector Grade Publications.
Senich, P. (1994). The Long-Range War: Sniping in Vietnam. Paladin Press.