Each week Nick Harvey answers shooters’ questions.
Q: After studying about six different reloading manuals, I’m puzzled at the variation in muzzle velocities there is with identical charge weights of the same powder. Some loads show a difference of 200 fps. How does this come about?
A: You should realise that the initial velocities given for various loads are intended only to show you approximately what you can expect. Most of the time an identical load will not come close to the listed velocity, even if your rifle has the same length barrel that was used in collating the data. Two different barrels, two different chambers or two different brands of cases can produce velocity results widely separated from each other, regardless of similarities in powder charges, primer and bullet weight. Another factor: some data is worked up in special pressure barrels which have minimum dimensions while others are worked up in factory rifles with looser dimensions. Then again we have different technicians using different techniques to measure pressure and velocity. Each manual is printed with great conscience. Time, expense and the firing of hundreds of rounds of reloaded ammo will go into the publication of a set of loads and velocities for a single cartridge. Careful attention is given to determining that the loads are safe, at least in the test gun. Then as a matter of extra precaution, the handloader is told to work up from the starting loads and not begin with the highest charges which are listed as maximum. It is important that each handloader works up loads are are safe for his individual rifle.