You'd be surprised what affects the speed of a bullet. Especially in a revolver round like the .38 special. Crimp is one big factor, along with cylinder gap. A chronograph can tell you more than speed, and sometimes the other things are more important, like extreme spread and standard deviation. If your Sd is small, then load is generally more accurate. If the Es is small then the load is generally more accurate.
So, if you saw velocities from 960-1209, we know that your extreme spread was pretty harsh. But, how was your standard deviation?
How far was your chrony from the muzzle. If you're too close, some of what you're measuring might be muzzle blast.