BALLISTICS
201. Where can I find further information on ballistics?
There is a ballistics calculator on the Norma website where you can see the parameters for various bullets, such as velocity, range, etc. You can also find this calculator in the Norma Ballistics App, for Android and iOS. Pure ballistics data is to be found in most manuals, such as the Norma reloading manual.
202. What is meant by the ballistic coefficient?
The ballistic coefficient (BC) of a body is a measure of its ability to overcome air resistance in flight. This coefficient is a relative value compared to a standard bullet with a BC of 1.0.
203. What effect does a short or long barrel have on velocity?
A long barrel results in a higher velocity, as the propellant pressure is significantly higher than the friction in the barrel. The velocity generally increases by 2-3 m/s per cm.
204. What is meant by twist rate?
The twist rate is often stated in inches (1 inch = 25.4 mm) and indicates the distance a bullet must travel down the bore to complete one full revolution around its long axis. Most calibers have a twist rate of one turn in 8 to 16 inches.
205. Why can't you use all bullet sizes in a particular gun?
Short (light) projectiles require less rifling in the barrel than long ones to achieve gyroscopic stability. Every bullet has a specified twist rate that is designed for certain projectile weights. Problems occur when you use extremely long (heavy) bullets and the twist rate is not high enough to stabilize the projectile. Example: the .308 Win has a twist rate of 12 inches. All bullets up to around 12 g are suitable. Heavier projectiles may result in an oval bullet path and reduce accuracy. Lighter projectiles receive more spin than they actually need, which is however practically without significance.
206. What should you take into account when shooting at low temperatures?
Test fire the gun at the temperatures to be expected on your shoot. Leave the gun to cool down for about an hour. You can either keep the ammunition in a jacket pocket or at the same temperature as the gun.
207. Why does the bullet flight path not correspond to the table data?
Before a true comparison can be made, the test conditions have to be exactly the same. The stand, the gun's firing position and the shooting angle all have to be same, for example, to ensure that the reason for different target locations is not something other than the projectile's flight path.
One reason may be that the velocity is not the same. All manufacturers measure the pressure and velocity of barrels that correspond virtually to the minimum dimensions both for chambers and barrels. This is done for safety reasons. Gunsmiths also try to prevent problems with excessive pressure and take certain plus tolerances into account in their dimensions. If these dimensions are greater than the ammunition manufacturers', there will be reductions in pressure and velocity.
Short or worn barrels naturally also result in lower velocity. In all probability there are bullet manufacturers who determine their ballistic coefficients with calculations and not with measurements after firing shots. If the BC used for calculations is too good (e.g. 0.45 instead 0.38), the projectile flight path obtained will be straighter than it actually is.
208. How far does a bullet travel?
It depends on the type of bullet, the velocity and the firing angle. Bullets generally travel furthest if fired at an angle of 30-34 degrees.
A .22 LR will fly approx. 1.5 km. A .6.5 hunting bullet can travel nearly 5 km and a heavy .30 projectile even 500 meters further.
In view of this fact, the target should be taken into consideration.