I'm sure this is somebody's official handgun drill or is a derivation of one, but it's an exercise I came up with one day when I had a limited amount of time for setup and practice. I think it's helpful for working on sight tracking, target transitions and reloading at the same time. It's simple, and you can run it with a revolver.
Spare mag or speedloader, mag/speedloader carrier, shot timer.
Set two IPSC, IDPA or any target with a typical vital zone at 10 yards, about three yards apart. At the signal, draw (or go from Low Ready if your range doesn't permit a draw), fire two rounds at one target, two rounds at the other target. Do a reload (speed or retention, your choice), re-engage the second target with two rounds and return to the first with another two rounds.
Start slow enough that all your rounds are A-zone hits and the reload feels unhurried. When it starts to seem easy, push yourself to go faster. Record your times to track your progress and note the threshold where you're no longer getting all hits. Slow it back down until the hits return. Once everything feels smooth- you're getting hits, the reloads go easy- start mixing it up. Change the target order (go right/left if you've been doing left/right). If you've been doing speed reloads, try retention or add a diagonal step to the rear during the reload.