Just wondering if anybody had any ideas on what the minimum velocity is to get hollow points to reliably expand. I use mainly XTPs and Hydra-shocks.

hollow-points can't be relied upon to expand reliably, there are many variables involved. that's why most experienced shooters prefer a large caliber with a wide meplat that doesn't have to rely on the unreliable to induce a high rate of energy transfer and cut a wide permanent cavity.

That sounds like the same logic as saying wad cutters have a sharp edge to cut through game. To answer the original question I'm not sure about a minimum velocity for expansion, I load target rounds and ball for pistol.

Some of the older literature (like Chuck Taylor's Combat Handgunning) indicate 1125 fps (or the speed of sound) as the speed you need for "reliable" opening of hp's. I believe the bullet manufacturers have probably adapted designs to reflect nominal velocities in the calibers they make so this may no longer have any real value as a guide. I guess faster is better for a hollow-point either way.

There has been great improvement in getting hollow pts to open. The Rem golden sabers are design to open as low as 575fps. The newer designs lets say from 1995 and newer well be the most dependable.

Deoneds on the caliber. Todays bullets have a pretty good vel. range for decent expansion. I've had 230gr RemGS expand well down to 700fps. What caliber are the XTPs? The XTP doesn;t expand much in any caliber, but they often expand within the individual calibers vel. range.