9mm velocity upset

[LiveLife]

Mystery Solved!!!

I moved my chronograph all the way to the target and instantly started getting normal readings. I had previously moved it a few times but only varied it from 8-12 feet from the muzzle.

Great. I love happy endings.

While different chrono manufacturers specify distance from muzzle (to minimize effects of muzzle blast affecting readings), I have found there are factors that can affect readings like ambient lighting, position of sun, etc.

One thing I have found is that closer the bullets travel over the windows on top of the chrono (Closer to the bottom of "V"), more consistent my readings have been. (And if you are afraid to shoot the chrono, you can use a piece of steel plate to use as deflector shield in front of the chrono with remote wire/bluetooth and app on your phone/tablet)

At 5:00 minutes, slow motion video shows different shock waves around the subsonic bullet and at 6:55 minute, video shows additional disturbances from muzzle blast closer to the muzzle (even individual powder granules can create shock waves)

 

[LiveLife]

even individual powder granules can create shock waves

This surprised me and further reinforced why we need to use chronos away from muzzle of barrel (Check out 4:15 minute for more clear slowmo video of powder granules creating SUPERSONIC shock waves from SUBSONIC load)