I carry a 642 Smith on a regular basis as a back up. Like Chuck, I have not seen any round tested in various medias including calibrated gel expand reliably. The only round I've seen expand at all was the 130 +P Bonded Ranger and even that wasn't impressive. The 135 +P Gold Dot I've seen open just a tad but not all the way. If I could get away with carrying a Full Wad Cutter I would but I have to carry a hollow point of some kind. I have a couple boxes of 135 +P Gold Dots at home but I carry Federal 158 SWCLHP +P in my snub. It's a hollow point so it fits our policy but cuts a wad cutter hole in people. I don't expect much expansion if any at all from it. The Gold Dot 135 is a good load also just felt like going old school this year and in the end we are really splitting hairs between these rounds. They are all better than the Police Widow Makers.
Off topic I have been around for tested for the 135 357 mag from a snub and found it expanded well. So did the classic 125 SJHP 357 mag from Federal. When we clocked them they gave us a 150-250 fps boast depending on the load compared to the 38 loads that were loaded with the same bullet. That little extra velocity does help to make a bullet designed for a 38 expand. I sold my 640 Pro years back because it was beating my hands. As Pat Rogers use to say "There is no such thing as a free lunch".