Seating for the plunk
When guys start reloading their own 9mm ammunition for competition or range use, they usually pull a load recipe straight out of a manual, set their seating die to the exact overall length listed on the page, and start cranking out hundreds of rounds. They assume that if the manual says the cartridge should be 1.150 inches long, it’s going to run perfectly in every single handgun they own. That assumption is totally fine if you only shoot Glocks, but the second you try to run that exact same ammo through a CZ 75, a Shadow 2, or a custom 2011, your gun is going to choke hard.
The mechanical reality of reloading is that the published overall length in a manual is just a rough guideline, not a golden rule. It completely ignores the distinct internal geometry of your specific barrel. Every barrel has a chamber, and immediately in front of that chamber is a section called the leade, or the freebore. This is the smooth, unrifled space the bullet travels through before it actually engages the rifling inside the bore.
Glocks and most polymer duty guns are notoriously over-bored. They have massively long leades, meaning you can load your ammunition incredibly long and the bullet will never hit the rifling early. But European guns like CZs, and precision-built platforms like the 2011, are machined with incredibly short, tight chambers and almost zero freebore.
If you are loading heavy 147-grain bullets to get a softer recoil impulse, those bullets are physically much longer than standard 115-grain bullets. The ogive—the curved portion of the bullet profile—starts much higher up. If you seat a 147-grain bullet to a standard 1.150-inch length and feed it into a CZ, the wide ogive of the bullet is going to physically crash into the rifling before the cartridge is fully seated in the chamber.
When this happens, the slide stops moving forward and fails to go into battery. If the slide manages to force the gun into battery by wedging the bullet deep into the steel lands, you have created a massive safety hazard. Because the bullet is already jammed tight into the rifling, it has absolutely zero jump distance when the powder ignites. The chamber pressure curve goes completely vertical instantly, creating a violent pressure spike that can easily blow out the case web or wreck your frame.
You have to tune the overall length of the ammo to match your specific barrel using the plunk and spin test. You take your barrel out of the gun and hold it vertically. Drop a loaded round into the chamber. You should hear a distinct, metallic "plunk" as the brass casing headspaces perfectly on the lip of the chamber. Then, you gently press your finger on the base of the brass and try to spin the cartridge.
If it spins freely and effortlessly, you are clear. If it drags, sticks, or requires force to pull back out, the bullet is hitting the rifling. You have to take that round back to the press, turn your seating die down a few thousandths of an inch, seat the bullet deeper into the case, and try again. You keep shortening the overall length until the round plunks perfectly and spins freely. I grab my reloading dies, calipers, and seating stems from https://www.brownells.com/reloading/reloading-dies/handgun-dies/ when I'm setting up a new press block. Your reloading manual doesn't know what gun you are shooting. Listen to your barrel, do the plunk test, and tune your length to your specific chamber geometry.