Check max COAL yourself in the pistols you will be using. Pistol throat lengths are all over the place, often even within a given model. Some are way long, while others are short.
There are different methods to determine maximum COAL. Some use dummy rounds or pinch in the mouths of fired cases. I do variations of that for rifles, but my preference these days for pistols is to simply load a single finished round. First, measure some cases I’ll be using and select the shortest ones. Size, prime, expand, charge, seat and crimp (be sure to crimp). However, leave the bullet seated out too long.
Crimping will not present a problem for incrementally seating the bullet deeper if you are crimping correctly. However, if you don’t crimp, remaining mouth flare can interfere with the plunk test. With auto pistol rounds you should only be “crimping” enough to straighten the case back out from flaring, not mashing the mouth into the bullet. These cartridges headspace on the case mouth. Further, overly crimping with a taper crimp actually reduces the case hold on the bullet. An overly heavy crimp mashes both the case and the bullet inward, then the case springs back outward but the bullet doesn’t as much, thus loosening the hold in that area as well as deforming your bullet.
Remove the barrels from the pistols you want to test. With the muzzle pointed down, drop your overly long cartridge into the chamber of each barrel. The long round will make a relatively dull thud sound, and when you try to rotate the cartridge with your fingers it won’t spin easily in the chamber. The bullet is making contact.
Turn your seating stem in a little, seat the bullet a bit deeper, and test again in the chambers. Keep repeating this and record COAL measurements as you go. When the bullet no longer makes contact the cartridge will drop into the chamber with more of a tinking sound than a thud, and you’ll be able to spin the cartridge freely when turning it with your fingers because it is seating on the mouth of the case without the bullet making contact with the throat or lands.
You can do another round or several the same way to better pinpoint or confirm the length where bullet contact is lost.
Keep in mind that case length affects the results. 9mm headspaces on the case mouth. By incrementally seating deeper you are changing how much of the bullet protudes from the case mouth, but case lengths vary.
Say, for example, that I get a max COAL of 1.140″ with a case measuring .750″ long. I then pull and reuse the same bullet with a case .740″ long. In the same chamber it would pass plunk at 1.130″ COAL because the same amount of bullet is protruding from the case mouth at that overall length. What really matters is mouth to where the bullet makes contact. For a given COAL, shorter cases have more of the bullet sticking out in front of the case mouth.
I use mixed range brass for practice ammo, and I’ve found occasional cases as short as .734″ before resizing. Most are usually .74-something. I like to allow a bare minimum of .015″ leeway from what I’ve determined to be max OAL (after using a relatively short case to find max) to be sure that a short case won’ t put a bullet into the lands.
The discrepancy found in 9mm throats is really annoying. If you have multiple pistols and one with a super short throat, you either load all ammo to fit in that shortest throat or label your rounds for what pistols various loads are ok for. That really sucks. One option is to ream the short throats to better match the others, which I have done. That’s not always an economical option now that more barrels are nitrided.
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