In practice I've met hunting and tactical weapons, based on this caliber to shoot superpretsizno but those razmyatat hits so I can not guess your shooting. Of course, at this point to have and the type of ammunition used, and whether the barrel "like" the present patron, such as pressure, depth of use of bullets and other factors.
Respect to the accuracy of a weapon is largely its total weight. Most tactical sniper weigh between 4.5 and 5.5 kg. Such weapons suggests moderate to good heavy barrel precision, but it is most comfortable to wear back in the long transfer, climbing and performing other physical activity. On the other hand this allows stable weight stop and gently hold the objective.
Of critical importance is the choice of bullet, outline (profile), length and pitch of grooves of the barrel.
When the use of .308 "Uinchester is a tactical view, the most advisable to use bullets in the range 9,7-12 grams. For long distances (600 m) high ballistic coefficient is not only desirable but also mandatory to reduce the influence of wind, gravity and drag bullets.
Numerous tests have shown that the .308 "Uinchester" lacks energy in their long-range shots. Therefore you should seek compromise on the initial velocity, ballistic coefficient, weight of bullets and energy. Over 600 m speed and energy of projectiles, respectively, decreased significantly in this caliber. For its part, the precision of .308 on short and medium distances is difficult to be exceeded by most other gauges. The effective range of a given size is determined by how far the bullet speed falls below the speed of sound (about 330-340 m / sec.). At .308, the average distance is 850 m
Recommended as a major bullet for this caliber I would definitely greynoviya 168 (10.89 d) of the "Sierra" hollow top and narrow rear (type boutteyl). He has a ballistic coefficient of 0.475 and a 66-cm tube can develop a speed of 850 m / sec. In the classic 60-inch barrels, speed is lower - about 830 meters / second. In the first case - a long tube - the speed of the projectiles will fall below the speed of sound at around 1000 meters. If you use a lighter bullet, which is 150 greynoviyat (9,7 d) "Sierra" ballistic coefficient of 0.440 and initial speed 884 m / sec, with scope nadzvukova speed is almost the same.
The various weapons and different lengths of cores would improve the range of .308, but he would never be a caliber to shoot over one kilometer. This does not mean that proektilat not hitting targets and larger distances, but the predictability and reliability fell sharply in these distances.
The step of grooves in the barrel is important for stabilizing the bullet. If we use 168 greynovi (10.89 g) bullets, 12-inch step of turnover (30.5 cm) is the ideal environment. If you do use heavier bullets, then you should go to a shorter step to a better stabilization - around 11 inches. To maintain a high initial speed of the barrel length must be between 66 and 69 cm
And now to stop the choice of contour (profile) of the barrel. It is known that the longer a barrel is, the higher speed gives the bullet. This is related to the full combustion of gunpowder. Accuracy of the barrel depends on its hardness or the resistance to its vibration. If a tube is long, it vibrates more, or we metaphorically call it "soft". To limit the vibrations need to increase the diameter of j. However, reflected in increasing the overall weight of the weapon. Here comes the engineering solution "two in one. The outside of the barrel is metal and takes receipt or orebryavane flutirane. So ribbed barrel retains a low vibration while allowing faster cooling, as is more surface.
Simple tactical sniper rifle and sporting weapons used cylindrical tubes, but sometimes tapered (a "varmint") are mounted on police and military rifles. If, however, distances of firing does not exceed 500-600 meters, and the rate of reproduction of the shots is more relaxed, you can go to a shorter and lighter barrel profile with and without cone orebryavane not expensive weapon. Recent trends are leading companies of urban snayperovi rifles to be mild, with short 50-inch barrels. When chuck diameter of the barrel is 30 mm, gradually narrows to 18 mm. If used longer, 660 mm barrel, then at 30 mm thickness is recommended to chuck 20 mm narrowing in dulniya section. Weight of the tube is about 2.5 kg.
The correct choice of barrel in .308 caliber is related to what it will be used. Whether the concept is a light rifle that would not burden her with the support redundant load or sniper who accurately drive bullets of 1000 m, depends on destination.
