How To Develop Plinker/Powerhouse Matched Pairs
Anyone who hunts large game needs a powerful load to do the job, yet the recoil from such loads can take all the fun out of practice shooting. Wouldn't it be nice to have a plinker load that had the same trajectory as the powerhouse load, but didn't pound the stuffing out of you? With such a pair of loads, you could use the plinker load to practice with and then change to the powerhouse load for hunting, without having to change your sight adjustment.
There is a way to develop such a plinker/powerhouse pair of matched trajectory loads. Remember, the trajectory of a bullet is determined by its muzzle velocity and its ballistic coefficient. Two bullets with the same ballistic coefficient will follow the same trajectory if they are fired at the same muzzle velocity.
To get a lighter recoil, the plinker load's bullet must be lighter than the powerhouse load's bullet, yet the two bullets must have the same ballistic coefficient. Therefore, the lighter bullet must have a more streamlined shape than the heavier bullet. One such pair of bullets is the Sierra Bullets 125 grain .308 spitzer with a ballistic coefficient of 0.340, and the Speer 180 grain .308 Mag-Tip with a ballistic coefficient of 0.352.
In a 30-'06, both the 125 and 180 grain bullets can be loaded to a 2,800 F/S muzzle velocity. If you enter these loads into the program, and zero them at the same range, you will see that they have nearly the same path all the way out to 400 yards.
Because the bullets will be fired at the same velocity and from the same gun, the relative recoil energy produced by these bullets can be estimated from just their weights. Under such conditions, relative recoil energy can be expressed as the ratio of the square of the weights of the bullets. For example, the square of 180 divided by the square of 125 is 2.07 (2.07 = 180² ÷ 125²). Thus, the powerhouse load produces slightly more than twice as much recoil energy as the plinker load.
Being able to match the muzzle velocities of the loads is the key to developing plinker/powerhouse pairs. The information in reloading manuals will help you get their velocities in the ballpark, but to dial them in and test their consistency, you need a chronograph.
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