Filler causes Chronograph to go haywire

[bhp9]

When using filler be aware that the filler when used with some loads, especially those loads that are traveling at below 2,000 fps. will often confuse a chronograph and make it go haywire.

Mine is a Chrony brand and it often fails to register any velocity at all or will flash a reading only for a split second. No such problem occurs when leaving out the filler. Others have reported the same phenomena when trying to chronograph black powder loads as much of the unburned black powder often causes the Chronograph to go haywire.

[ANeat]

Yes you have to move the chrony farther away from the muzzle if you want to get a good reading

[JeffinNZ]

AND make a polycarbonate face plate for the Chrony to protect it. Mine took a hit from an errant gas check and was out of action for a few months.

[runfiverun]

all i have to do with mine is keep the sun outta it's eyes.
and the wind from tipping it over.

[BerdanIII]

Don't forget bugs; one day a bug flew over the back cell and a split second later his buddy flew over the front cell for a combined BV (Bug Velocity) of 6000 fps. People at the range were impressed.