It really depends on the type of shooting match your talking about. A "Spot Shoot" in my neck of the woods consists of shooting at a stationary paper target at a 25-50 yard range to see who can place a shot closest to the bullseye. Obviously your going to want gun that will create a tight shot pattern, full choke or even a turkey choke added will greatly increase the chance of placing a single shoot near the bullseye. Shotgun barrel lengths are primarily in the 32" range, but I've seen many custome designed barrels as long as 40" that required a resting stand to support the barrel length. Some Sportsmen's clubs have their own local rules related to barrel length. The key is finding that favorite shotgun in your gun chest that consistently develops a very tight shot pattern.
The question can't be answered without knowing what type of shooting and what "gun" you mean (hand gun, long gun, centerfire, rimfire, muzzle loader, etc..)
At a shooting range is usually the best choice.
That is the National Shooting Sports Foundation. They promote shooting sports. Gun control attempts to prevent ownership of guns used in shooting sports. No gun= no shooting sports.
Head or Heart shot
A shooting iron is a gun.
The slowest shooting machine gun ever made would have to be the Colt 1895 best known as the Potato Digger. It had a rate of fire of only 400 rounds per minute.
Use helium balloons, let them go and shoot them with you chosen gun.
by shooting it with a gun.
practice
Shooting solder at a special solder shooting range
Gun clubs, shooting ranges
The Gatling gun.