I believe the 'issue' was the 38/44 which was the larger frame revolver. It is a .38 Special which is why the 1911 was popular in .38 Super. Yes, some chose the 1911 as did many of the bad guys since the makers of 1911's, BAR's, and Thompsons were all looking for a market after WWI (yes I know the Thompson was not invented until 1928, my point was the Auto Ordnance was still searching for customers). The .357 that came out in 1935 was 'issued' to at least one FBI man, J. Edgar Hoover got SN 1 (or some other very low number) with a 3.5" barrel. The .357 was superior to the .38 Super against cars.
By 1955 when my father entered the Bureau they were issuing 4" tapered barrelled mod 10's (K-frame) or the Military & Police as it was called. It was not until about 1979-1980 that they began to issue the mod 13 with 3" barrel (.357 fix sighted K-frame). My father retired in 1977. After 1981 there were SIG's and the S&W 1066, though I have never met or talked to an agent who was ever issued one, and Glocks. In the early 1970's I did meet three agents who did not carry any of the approved revolvers, one with a S&W mod 39, one with a mod 59, and one Browning HP. I never saw those agents on the range qualify with any of those guns, they always shot the mod 10's or a mod 19 that they purchased themselves. The vault also had a variety of Walther PPK .380's and S&W mod 49's that could be checked out by agents on undercover assignments. That was in the early 1970's, I know the mod 49 was available in the 60's, but I didn't see any Walthers. The Mauser 98 rifles were replaced around 1971 with the Remington 760 (or was it a 742, it was the pump rifle in .308 with a 4x B&L scope). The Mausers in the OKC office, about a dozen, were all sent to Tinker AFB and chopped up into little pieces. When the M16 replaced the Thompson SMG around 1973 or 74 each office was allowed to keep a couple for show with the neat hardcase, but all the rest were sent off to Tinker to be hacked up also.