The movie Alatriste made a pretty epic depiction of the reiter cavalry armed with pistols (0:50). However they start firing way too early. The reiters would need to get very close to the enemy as the pistols were not that accurate and powerful yet.
There were saying such as that reiters need to get as close to the enemy before shooting that the blood would spill over them, or so that they could see the white in their eyes. Of course this is rhetorical but it captures the spirit of this type of warfare.
Another thing I noticed which I think is flawed in this otherwise great scene is that the reiters crowd the tercio from all sides instead of using a "caracole" (rotating in front of infantry in circle and firing one by one) or similar more disciplined approach.
The reason why caracole was effective was because it kept continuous pressure on the enemy pikemen and also gave reiters space for a potential charge or to pick off individual units. But in this scene they just stop close to enemy pikes and lose the momentum, ending in stalemate.
Reiters were armed with multiple pistols so that they could fire more shots. Usually they had two or three pistols, but some had even up to six (four in holsters and one in each boot)! So they could keep firing for quite a while if they used a disciplined approach.
Some caracole tactics were also used in such a way that the reiters could reload their pistols on their horses! Here is a depiction of such tactic! Reiters fire in front then move back to a steady line to reload, and are then ready to fire again! Very clever, isn't it? 
• • •
Missing some Tweet in this thread? You can try to
force a refresh
