Hank Sloan was more than 'just' an FBI agent and holstorians are interested in the holster that he created for his agency's use and was made by J.M. Bucheimer beginning in the mid-1960s and even after his death mid-1970s.
Less known, because I had a collector contact me recently, is that there were several variants of the Sloan holster that included how it was marked, what leather it was made from, and with or without safety strap (which I expect was for the final years of production). It's a holster best judged by collectors from its backside.
The brown ones below are made from full-grain leather and a finish applied. This is the very best of veg tanned leathers vs the way the black leathers were curried for J.M. Bucheimer.
The black gunleather for J.M.B. was made of top grain leather; this is not the equal to full grain leather and is painted. The simple way to understand the difference, though it could get a post of its own, is that the grain side of leather is where the hair was and the opposite side is called the flesh side. When that grain is left undisturbed it is called full grain; when it has been sanded, filled, and painted it is called top grain and this is what J.M.B. used for black. Notice the brown edges of the belt loop: effectively having been dyed and finished at the tannery before the parts were die cut, the leather was a natural color through its thickness and here the black paint has scraped off the surfaces with use.
The strapped version, perhaps in reaction to agents like Bill Rogers failing to keep the tensioned welt adjusted (which is why it was invented, by the way) and losing their revolvers from the Sloan, below. Even the marking suggests this is late in J.M.B.'s production of it. It disappeared from the line by the late '70s but then so did sister company Bucheimer-Clark; then J.M.B. in the '80s.
Sloan conceived it but did not develop it, and this leads us to discuss, someday, the difference in what men call 'designed' vs 'created' vs 'invented' vs 'engineered' vs 'perfected'. In this case let's say that Sloan, who was not a gunleather man, had his invention perfected by J.M.B.'s captive designer who was Al Kippen. And the Sloan looks much like a Heiser 459 because, well, Kippen created that one, too; for new owner Keyston Bros in 1960 and the 459 preceded the Sloan. Kippen went on to do more of the same for S&W Leathergoods which is where he landed, staying while it changed into Gould & Goodrich then retiring and dying.
Read more in my book titled "Holstory -- Gunleather of the Twentieth Century -- the Second Edition" that is available at www.holstory.com and printed for you/shipped to you in USA.