Quote Originally Posted by angrybear View Post
Yes it does but it needs the unit to be stationary so the return delay time from several signals at pre-set intervals can give the velocity.
If the unit moves back & then forward again with the recoil, the signal delay will falsely increase as the unit goes back extending the nominal distance to the projectile,
then falsely decrease as it returns forwards fractionally decreasing the nominal distance to the projectile.

So the projectile will appear to start off faster than it is, then appear to slow before speeding up again, that's going to confuse the computer maths & give a false reading.
Ah yes. I get it now, thanks.

I have seen them being used off the rifle, just below and back from the muzzle. So guess this is the solution for the OP (and maybe what is noted in the thread link above?).

Rich.