Match grade barrels are built to very high standards for accuracy. The ability to shoot shots very close together is the difference between a match grade barrel and all others. Most rifles bought from a gun store or manufacturer are not built to match the accuracy of match grade barrels. Although they are still good products, they cannot produce the superior results of a barrel that is match grade.
Match grade barrels are made to be extremely accurate. In the shooting world, accuracy is defined by something called "Minute of Angle" or MOA. The easiest definition is that however close a marksman can put three to five rifle shots together in a group produces the MOA. At 100 yards, if the group of shots is measured inside 1 inch square, the rifle is considered accurate to 1 MOA. If the shots take up 2 square inches, then the barrel is accurate to 2 MOA. The MOA measurement is also dictated by distance. One MOA at 200 yards is 2 square inches. At 300 yards, the square for 1 MOA is 3 inches. A match grade barrel is built for accuracy and should produce rifle shot groups of 1 MOA or better. Some match grade barrels consistently produce shot groups measuring as little as 1/2 MOA.
Match grade barrels are used almost exclusively by competition shooters and snipers. Rifle matches are sometimes out to distances of 1,000 yards. One MOA at that distance is 10 inches. If a shooter can get a barrel with a 3/4 MOA he has reduced his group of shots to 7.5-inches, and 1/2 MOA reduces it further to 5 inches.
Sniper rifles are made for extremely accurate fire. Army and Marine snipers have carried bolt-action rifles for many decades. In Iraq and Afghanistan, sometimes there is a need for a rate of fire beyond that of a bolt action rifle. Sniper teams have been carrying semi-automatic rifles with match grade barrels as well as bolt action rifles with similarly equipped barrels.
A match grade barrel is extremely accurate because it is built to exacting tolerances. They tend to have a tighter barrel than those found in average rifles. This difference means better accuracy. One way of looking at it is comparing it to a thrown football. The match grade barrel produces a tighter spiral than its non-match grade counterpart. The tighter spiral is the result of the barrel's being more close-fitting to the bullet, producing a more accurate barrel that produces better shots.
Match grade barrels can be extremely accurate. Typically, the casual shooter is not a good candidate for a match grade rifle. Generally, the rifles are more expensive than their non-match grade counterparts. Also, the need for such extreme accuracy is rarely needed by anyone who is not either a competitive shooter or a military sniper. Practicing proper fundamentals is the best way to improve accuracy for most shooters. If you decide to become a competitive shooter or a military or police sniper, the match grade barrel will help tighten your groups of shots on the target.