were do you get a good velocity measuring device? Answered

You can make a ballistic pendulum for almost nothing. Shoot the pendulum, measure how far it swings, do some maths and out pops your muzzle velocity.

One thing that may work, mythbusters once used stick-on accelerometers. You can buy them for cheap, in large numbers and different levels of resistance. You could put a piece of wood and put some on it, then shoot it. That might work. Hope i helped!