I use a magnetospeed on the barrel and a Chrony at 10 yards. Then I write the data down for each and compare and contrast afterwards.
I'm completely tracking what you're saying about consistency with shot-to-shot velocity, especially as it applies to the far targets. I only PLAN on shooting this gun to 900-1000 or so, so every little bit helps. My biggest constraint is actually the OAL of the mag (It's an LMT MWS, so it takes PMAGs).