Last I heard, Houston PD does not issue guns, officers supply their own. Don't know about revolver use, though
As I understand it, they do provide their own guns and up until a few years ago, could get whatever they wanted. Now, graduates from a certain year forward they still buy their own guns but the gun has to be a .40 caliber auto. Prior to that year the older men can still carry their old guns whatever they may be (.38 Revolver or .45 Auto or whatever) and are grandfathered out over time