If you are like most shooters, you have noticed that certain ammo does not shoot well out of certain rifles resulting in lousy shot groups. Contrary to popular opinion, the problem isn’t the ammo or the gun. The problem is barrel surge caused by the shock wave. When you pull the trigger, the firing pin strikes the primer which ignites the powder and creates an explosive force that drives the bullet down the barrel. This explosive force also creates a longitudinal shock wave which travels up and down the barrel up to six times before the bullet exits the barrel. It is likely that the bullet is exiting the barrel at the same time that the shockwave is reaching and expanding the end of the barrel. Because the bullet exits the barrel when the barrel is slightly distended, the bullet is free to slightly vacillate. And this is what causes the inconsistent shooting and loose groups.