Up until a couple years ago, my PD let you carry pretty much what you wanted, within policy (no SAO, calibers 9mm, .38+P, .40 or .45, reputable manufacturer, inspection by armorer). I carried an older 2nd Gen G21 for almost 20 years. Back then, .45 made a lot of sense since hollow point technology back then meant that they often failed to expand. Not to mention, the Dept bought the cheapest hollow point ammo they could find. The reasoning was if it isn't going to expand anyway, why buy expensive ammo?
A couple years ago, I made the decision to go to 9mm in a brand new 3rd Gen G19. Literally a week after I bought the gun, the old Chief unexpectedly left on a medical retirement. New Chief decided to issue guns and, instead of listening to the head instructor (namely, me) he decided to issue Gen4 G22s. I HATE .40, so of course I hated the issued guns. To be fair, the G22s are VERY accurate and reliable. If you like .40, they are a very good choice.
About 6 months later, new Chief becomes City Manager and we get another new Chief. He's been Chief for about a yer and a half and has decided that he doesn't like .40, either and started carrying his old, VERY early 2nd Gen G17 (old as in 2 letter serial number prefix old). Policy is slowly switching back to carry what you want within reason.
So, when we qualify again, I get my wish and will carry my G19. 9mm ammo has come a LONG way in the past decade or so and there really isn't much difference between 9mm, .40 and .45 anymore, as long as you use good ammo, which we now do (I'm buying Speer Gold Dots for duty ammo; 124+P in 9mm, 180gr in .40 and 230gr in .45). Same capacity as my G22, lighter recoil, quicker follow up shots, smaller overall size and slightly lighter overall weight, cheaper practice ammo (Dept DOES NOT provide any practice ammo), all in a gun that I shoot as good or better than the G22. As an added bonus, it is small enough that I can carry it off duty during the fall/winter, when I wear heavier cover garments. Overall, a win/win for everyone. Keep your issued .40 if you want, carry something else if you don't like .40.
Bub75