I've worked with some who were carrying either Glock 26 or 27, didn't ask which but they were the small ones. They weren't issued.
In the 70s saw various wheelies being carried. The issued back then was the pencil barrel 4" S&W Model 10. The 2.5" Model 19 was very popular, along with 4" Model 19, 36, 49, 60, and 66 both in 2.5" and 4". For the Colts guys would buy Dick Specials. 1 guy carried a Diamondback. Don't recall ever seeing any other POW Colt altho 1 agent kept telling me he was going to buy a Python. Some of the old timers still carried their issued Colt 4". Knew one who carried a 3.5" Model 27. Autos weren't authorized back then, however, knew 1 who carried a S&W 59 and another who carried a pair of BHP in shoulder holster with one under each arm. Neither were authorized weapons. Hoover was of the opinion that only criminals carried autos.