QUOTE: A plainer version of the Colt Cobra as I understand it.
The only difference between the Agent (introduced in 1955) and the Cobra (introduced in 1951) is that the Agent was made with a slightly shorter grip. Starting sometime around 1966, both revolvers were made with the shorter grip but the Cobra had longer stocks, overlapping the grip. The finish and workmanship were the same for both.
"Second Issue" D-framed Cobras were made from 1973 to 1981 and they came with an ejector shroud and a long ramp front sight. During the "Colt strike", Cobras were offered with an unpolished, matte-black finish. The coltfever.com website reported, "...These post-1972 Cobras were the only version that Colt ever rated for use with +P ammunition. The gun was rated for 'up to' 1000 rounds of +P ammunition, after which time the gun was to be returned to Colt for inspection and possible frame replacement."