I did have one question, though. What happened at shot #346? It appears as if something was changed causing a few low chrony shots and higher SD values. However, this could be caused by paint size variation. Also what was shot #347? Was it a low shot? Is that why it was left blank?
the blanks are when we missed a chrono reading. Usually it's when the second eye on the chrono didn't see the ball. It happens sometimes. shots 61, 85, 320, 347 etc.
I kinda see what you're saying about 346 - but actually it's only 3 lower than 345. All guns have odd shots from time to time. This one is no different. I wouldn't try to read too much into any one shot - it's the means and SD data from groups of shots that really starts to have meaning.