250 and 255 are basically the same. You can use their data interchangeably. Some 250 gr. bullets I've weighed are actually closer to 255 gr. anyway. And with standard SAAMI pressure 45 Colt (14k psi) in a Ruger, even the mid-frame, you have a pretty wide range to play in, especially with a medium burn rate powder like Universal.
What's more critical is amount of bullet inside the case, but that's generally not an issue unless you're loading really heavy bullets at max velocities. Or when you're looking at a Hornady XTP, which has more bearing surface and more bullet inside the case than most. In fact, you can usually substitute XTP data for a similar weight bullet, because the XTP presents the worst case scenario of pressure and seating depth.