The immense heat, pressure of burning powder and the abrasive nature involved in sending thousands of rounds down range in practice and in matches will take their toll on the guns accuracy and eventually the barrel will need to be replaced. An important piece to keep in mind is that barrels in the competitive rifle shooting world are consumable items. You simply cannot get the practice in without wearing out a barrel, a tough pill to swallow but a necessary one in order to get where we want to go.
A rifle barrel is constantly changing throughout its life from the first firing until the day its accuracy is deemed no longer competitive. The immense heat and pressure from shooting causes changes your barrel in a three layered cross section. The initial surface layer that is in contact with the heat, pressure, and erosive gas from the burning gunpowder and this surface area actually undergoes chemical changes to the molecular make-up of the steel.
This layer is extremely hard yet due to how thin it is, is very delicate. This first layer is what protects the underlying steel of our barrel. It should always be our goal to keep our influence on this layer minimal and as intact as possible since it has the most influence on our bullet and can be susceptible to damage with harsh abrasive cleaning agents. The second area that is effected lies underneath this first layer and in a perfect world does not come in contact with the bullet, yet is still close enough to the bore to be affected by the heat generated while shooting.
The third area is the outermost area of a barrel that is shielded from chemical and heat changes and usually has little change through the life of a barrel. Both the chemical changes and changes due to heat weaken the barrel steel in the bore to a point it is more susceptible to the erosive effects of burning gas which accelerates wear. Shooting accuracy is measured in units known as minute of angle, or MOA.
This is a geometrical measurement, but in practical terms if a good marksman can put a group of five shots into a one-inch square at yards, the rifle is considered accurate to 1 MOA. If the group of shots covers two inches square, then the gun is accurate to 2 MOA. The greater the distance, the larger the target grouping can be. HBAR stands for heavy barrel, or heavy barrel automatic rifle. This type of barrel has a consistent heavier barrel wall thickness than standard issue, and is a common upgrade for AR15 type rifles.
The heavy barrel dampens harmonic vibrations as a bullet moves through the barrel, so bullet groupings at a distance are tighter, and the MOA is smaller. A true match grade barrel is very important for competitive shooting, but that is about it. However, make sure you actually need to spend this extra money before buying one.
If you are just doing some casual shooting or hunting, you are going to be fine with any barrel. However, if you are doing competitive shooting or extremely long-range hunting, a high-quality barrel is going to vastly improve your abilities.
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