http://www.evanstarget.com/pages/5/index.htm
My favorite reactive target is a Shaffer Shifter made by the folks in the link above. I have a couple of different sizes with different thicknesses to use based on the gun and caliber being shot.
The target is hung by a chain from a tree limb or cross bar. Mine are hung from about 15 feet up. To start, you simple start the target swinging, step back to an appropriate distance, and then shoot. As bullets impact, the swing will change in speed and direction. Since the target swings free, it continually changes position along 3 dimensions, mostly in distance from the shooter and laterally. However, because it swings at the end of a chain, it continually is changing elevation as well. While in motion, it will spin after being hit. Since it has target planes on both an X and Y axis, it is three dimensional. So, the spinning of the target does not preclude shooting at the target and the shooter does not have to shoot form a particular direction relative to the target. So the shooter can work on shooting on the move without losing a target face as can happen with simple flat targets when the shooter moves too far laterally.
As with the Temple Texas incident and the North Hollywood Bank robbers, shooters often talk about the difficulties in making head shot on moving targets. No doubt there is some very real concern in that regard. Those moving targets (heads) are apt to move in any axis and few folks have a way to shoot targets that would be comparably difficult short of simunition training. The shifter target is a pretty darned good training substitute.
One thing that I have found in introducing folks to the shifter targets for the first time is how difficult the targets seem to be to shoot by the new shooter, even if the shooter is experienced. This aspect indicated to me that concerns over shooting small moving targets (such as heads) is really very difficult for somebody who hasn't had to deal with that sort of moving target, such as folks who do a lot of typical IDPA, IPSC, or even 3 gun shooting. The frustration on the face of a shooter becomes readily apparent by the end of the first magazine. One friend in particular who could easily shoot inside a 6" circle of a stationary target at 10 yards blew threw 40 rounds of .45 acp with only 4 hits on the 6" shifter. After a quick break and reload, the notion of dealing with a small target in motion sunk in and he wsa able to hit about7 or 8 out of every 10 at 10 yards.
We also tried carbines at 25 yards. With an AR15, he did much better with his first couple of mags than he did with a pistol. By the fifth or sixth mag, he was doing extremely well. So I changed him over to a Beretta Storm carbine in 9mm and he immediately started missing most shots. What was the difference? Not the gun, but bullet velocity. At 25 yards with a .223, if your sights are properly on target and you are aimed anywhere other than the rear edge of the target, then the slug was able to travel the 25 yards and impact the target without the need for leading the target. With the 9mm round, it became necessary to am a couple of inches ahead of the center of the target so as to compensate for target motion and the much slower velocity of the 9mm round. Once he discovered the need for leading the target, his hit rate rose dramatically.
In timing the full lateral swing of the target from one side to the next, the target was traveling between 4 and 8 mph. It was closer to 8 mph when the target swung perpendicular to the shooter. When the aspect of the swing to the shooter changed, such as swing at an angle .45 degrees from perpendicular, the lateral speed from left to right was slower from the shooter's perspective, but the distance from the shooter was changing.
The shifter target is a nifty target to have for fun plinking and for defense shooting drills. The one limiting aspect is the need for having a location and materials from which to hang the target. I used trees in two different ways. The first was to simply hang the target from a high limb about 10 feet from the tree. The second was to string a chain between two trees that didn't have limbs suitable for hanging. So, the target was hung by a single chain attached to the chain strung between the trees.