Tried shooting through a buddies chronograph today, what a disaster. Didn't matter what muzzleloader I shot the speeds where anywhere from 640fps to 3680. Shot two different centerfire rifles and both worked normal. tried anywhere from 6ft to 12ft from muzzle, tried with upper shrouds on and off. nothing made any difference. Next time he comes out what should try?

Try putting the chrono at least 15 feet. Were you shooting patched balls, conicals, or sabots?

If you were shooting sabot, that could be your problem. My clock reads the last thing through. At the range of your clock location, the sabot probably have separated from the bullet, and the clock read the speed of the sabot, and not the speed of the bullet. When shooting where i can find sabot, i start finding them on the ground around 8yd out, and don't find any more beyond 20yd. I normally put my clock near 20 yard, and use a ballistic program to calculate muzzle velocity working backward from the 20 yard velocity.

I tried maxi balls,sabots and round balls. looks like I should move back to 20-25 yards.

I agree sabots can be the cause and so can other things, even parts of unburnt pellets. One of the loads i would really like to chrono has a bad habit of slow sabot separation. Many sabots go 20yards with this load.

Great care needs to be taken to make sure sabots dont hit the chrono too. They will cause far more damage than some might imagine. A couple companies make boxes to help prevent chrono damage too.