The Colt-branded A.R.M.S. #05 Multi-base Mount was used on the Colt Sporter Competition HBAR “Range Select” rifle which replaced the AR-15A2 Delta HBAR in 1992 (information provided by Small Arms Solutions). You can see more information on the R6700CH Sporter Competition HBAR here on The Colt AR15 Resource at this link: https://thecoltar15resource.com/r6700ch-range-select/ .
I do not know if the mount was ever marketed as a separate accessory.
The following information is from the Atlantic Research Marketing Systems (A.R.M.S.) website at http://armsmounts.com/shop/mounts/a-r-m-s-05-multibase-mount/
A.R.M.S.® #05™ Multibase Mount NSN 5855-01-491-3604
One of the most versatile mounts on the market. Made of extruded aluminum with a Mil-spec black hard coat. 100% MADE IN THE USA.
The #05™ Multibase is a Quick detachable, multiple eye relief mounting base that attaches to weaver type rail and flat-top receivers. The multibase is compatible with both weaver style rings and NATO STANAG mounts. It raises your sight platform 3/4″ and features a spring loaded clamping bar and self locking captivated thumbnuts for solid, zero movement mounting to your existing rail. The #05™ multibase also features a see through channel for use with iron sights. Also available with Throw Levers® – see #63.
Weight – 5.2 oz
Length: Approx. 5″
Height: Approx. 3/4″
The A.R.M.S. #05 has been out of production for many, many years and was replaced by the A.R.M.S. #36 throw-lever mount.