During the 30 years when I was County Undersheriff and Chief of Police, I gave my deputies and officers the option of selecting their personal duty weapon, so long as it equaled or exceeded a .38 special. I required every one to fire on our range monthly and strictly qualify every 3 months.
Over the years, my 60+ LEOs used numerous handguns, semi autos and revolvers, some trying more than three or four over time. Personal reasons prevailed, including physical ability, comfort carrying, required ability to strictly qualify, dependability, etc. I remember that over the 30 years, only about 5 or six actually carried semi-autos regularly after trying and using various weapons. Of those I believe all were .45 ACP's.
The most common handgun carried by my LEOs was the Model 19 S&W, .357 Mag after trying numerous other models and calibers. The second most common carried by my LEOs was .44 Specials, Colt or S&W. Some of the LEOs, carried +P.38 Special ammo in their Model 19's. I remember one Deputy that I had for over 25 years. He developed arthritis that made it uncomfortable shooting and qualifying with his .357 Mag. By substituting .38 Specials in his model 19, Wad Cutter Target Ammo, he was able to continue working and qualifying.
I have mentioned here that my wife regularly carries and regularly practices with her Charter Arms, rubber grip .44 special, as she has for 50+ years. Over the years she has tried almost every one of the handguns used by my officers when I was in charge, plus numerous others owned by friends. She is an excellent shooter and has always stated that her .44 special suits her the best that she ever tried. I have carried and used my two .44's since 1958 and 1961. I believe I have tried perhaps 40 or 50 different handguns in my life. I never found any better than my .44's, my S&W model 29 on duty and off, or my .44 Ruger Blackhawk when on horseback working on my ranches.
I know that many, perhaps most departments require all officers to carry the same ammo and/or weapon model. There are valid reasons for this, including economics. But I have noticed that most, especially large departments, have never required the strict qualification specifics that I required when it was my responsibility for all my LEOs.