Shootist and family: when are you starting a top using bullets?
I looked a little more into this.
I found on Wikipedia that a 0.22 LR bullet (apparently the most commonly sold) has a nozzle velocity of 533 m/s, a mass of 2 gr. and typically spins at 78,750 RPM
One way of spinning a top with a bullet would be to hit it in the perimeter so the momentum of the bullet creates the torque to spin it.
A little bit calculation gives me that in the best case, for the bullet being lodged at the rim of a small top (i.e. a Gladiator), it could make it spin at around 10,000 RPM. So it is theoretically possible, but my guess probably quite difficult, to spin a regular top with a bullet. However, a special target spintop could be designed for this.
Another way to spin a top would be to transfer the rotation of the bullet to the top. I get that the rotational inertia of the bullet is about 100 times less than that of a small top. So, if the bullet was shot down through the crown and became lodged inside the top, to conserve the angular momentum you have to divide its rotation by 100. The Gladiator would spin at less than 800 RPM: not enough but close. A faster spinning bullet could theoretically do it. According to the rifling article on Wikipedia, a bullet from a M16A2 rifle can spin at 314,000 RPM, what would give about 3,000 RPM for the top. In practice, however, you would need to stuff the top with something heavy to stop the bullet, what would increase its inertia, so it may not work after all . . .