@kluthe: If you go to the Hodgdon Reloading Data website, you\’ll find AutoComp loads for 124 gr Berry\’s and XTPs. The former OAL is given at 1.150\” and for the latter at 1.060\”, and charge weights ranging from 4.5 to 5.4 gr. That window is narrow enough to keep folks out of trouble.

As for the OP, chronographs vary from user to user and brand to brand, and atmospheric conditions affecting air density (like altitude, temperature and even humidity to some degree) will alter velocity measurements. As an example, I have yet to see a Lab Radar record a lower velocity for my 9mm and .45 ACP loads than my dated Chrony, which is a conservatism I appreciate for major matches. However, this powder was designed around race guns using compensators (hence the name), so it wouldn\’t be my first choice for general purpose target shooting or competing in divisions where comps are not allowed.