goodies from USG

[Technician1002]

Yup. It's a lot easier to spin a small mirror than it is to spin a whole stinkin' camera.

Quite a bit of timing precision needed though.

I have the materials to do this type of stuff except the expensive high speed camera. To move the mirror on command at high speed, a Galvanometer is used with a feedback winding. This is the same class of servo system used to paint with laser light for laser lightshows. Given the known projectile velocity and path, the path of the mirror can be pre-programmed and triggerd by the projectile exiting the muzzle.

For more information on this galvo servo and the positioning speeds possible, google search Laser Galvanometer with feedback. The closed loop feedback gives them the positioning accuracy.
http://en.wikipedia.org/wiki/Laser_projector

[D_Hall]

As tech said, it's not a big deal with current tech.

But even with old school tech it's not that big of a deal.

1) Get a mirror that spins at a constant speed.
2) Using anticipated velocity, determine how far away mirror should be to track the projectile reasonably well.
3) Spin the mirror, start recording and fire the gun.

You won't get the nice "watch the muzzle until something moves" view that the modern stuff will, but you can certainly get your projectile in flight. The only trick is firing the gun at the right moment which can be done reasonably simply using an electrically fired gun that takes a signal from the spinning mirror in the same vein as an old-school automotive distributor cap. It may take a couple shots to dial in exactly when to shoot, but the point is that it's easy to do with tech that was available as early as the 1930s.