When reloading for "match grade" shooting, l one thing to keep in mind is the effect of the pressures on the brass cases. You want every cartridge to produce the exact same (well, as close as you can make it, there isn't really a perfect) muzzle velocity. Think of the brass cases as a "pressure vessel". One type of pressure vessel we can all relate to are rubber party balloons. If you bought a package of 6" balloons from one company, and a package of 6" rubber balloons from another company, and put exactly 3 psi of air pressure in each balloon, they would expand to a different diameter. That's because each company's manufacturing process would be slightly different, including the formulation for the rubber compound.

In exactly the same way, the brass cases of one manufacturer are made differently than another. When fired in the chamber, two different head stamped cases will expand in the chamber slightly differently. Each producing (presuming that the amount of powder, bullets, primers, etc are all exactly, or as close to exact as you can make them) a different muzzle velocity. With the force of gravity acting constantly, the slower bullets will hit lower than the faster bullets. So, in match grade pistol shooting (trying to hit a 1" sized target at 75 yards), the matching of the head stamps make a HUGE difference.

When I started shooting this chambering size, I didn't have enough of any head stamp to focus on any one of them. So, I invested in 1,000 Starlines, brand new. And, rotate those through my inventory and cartridge assembly.

For normal pistol shooting, you should not have to match head stamps like I do.

Also, please note that for precision rifle shooting, the only pathway to highest accuracy is also to use matched head stamps. In the longer rifle barrels, where the velocities can really build up, the muzzle velocities are very important to maintain.

Hope that explains why I use matched cases for SOME pistol cartridges. I assemble thousands of, for example, 9mm Luger and 357 Sig. I have never sorted those for head stamps. They shoot just fine in the mixed condition. I don't ever shoot those in any sort of match grade shooting.