The effects of different primers on ammunition accuracy is a topic that interests many, but which relatively few can easily test with precision. Most competitive shooters are limited in their access to a 1000-yard range and a quality accuracy-testing facility. Thus, experimentation with primers is often done at shorter ranges, relying heavily on chronograph results to help select primer brands or lots by velocity uniformity and accuracy testing.
The U.S. Army Marksmanship Unit discusses necking cartridge cases up and down, the differences in cartridge concentricity (runout) that occur based on one’s method and some “fixes” that can reduce runout as we load.
A quality tool for measuring TIR is essential for obtaining consistent, accurate results. Generally, measuring equipment is not a good area in which to skimp or economize, as one uses these tools throughout one’s handloading career. They form the basis for consistent reproduction of accurate ammunition lots.
Having sized, primed and charged our brass, the next step is bullet seating. Many approaches are possible; one that works well follows. When setting up a standard seating die, insert a sized, trimmed case into the shellholder and fully raise the press ram. Next, back the seating stem out and screw the die down until the internal crimping shoulder touches the case mouth.
Even within the same caliber (e.g., .223 Rem. or .308 Win.), there are many different chamber designs and each can require different COALs for best accuracy.
In Part 1, we measured the pre-firing bearing surface length. When the bullet is thrust forward upon ignition, it is pressure-swaged to fit the bore.
How to avoid pressure problems when developing loads.