Thread: 9mm reloads
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Old February 29, 2012, 02:50 AM   #24
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Join Date: June 12, 2010
Posts: 475
You do not need to use the OAL listed on published load data as often test barrel fixtures and not real pistols are used to measure chamber pressures. Using published OALs WILL NOT ensure reliable feeding/chambering of finished rounds in your pistols.

Determining OAL should not be a guessing game and I use the following process for semi-auto loads whenever I use a new bullet:

1. Make sure resized cases drop freely into the barrel chamber. If not, adjust the resizing die to ensure the cases are resized full-length and fall in freely into the chamber.

2. Determine Max OAL - Make a dummy round (no powder/primer) and perform the barrel drop test with the barrel out of the pistol starting with the SAAMI max OAL until the dummy round falls into the chamber freely with a "plonk" and spin without hitting the start of rifling. To determine the amount of taper crimp to return the flare back to flat, I usually add .020" to the diameter of the bullet (So for 9mm .355" diameter bullet, .375" taper crimp and for .356" bullet, .376" taper crimp).

3. Next determine Ideal OAL - Load the Max OAL dummy round in the magazine and manually release the slide without riding the slide with your hand. Incrementally decrease the OAL until dummy round reliably feed/chamber. Depending on the pistol/barrel used, Ideal OAL that will work reliably will vary. If you are reloading for multiple pistols, use the Ideal OAL that will work reliably in all the pistols.

9mm cases headspace on the case neck edge/mouth and length of leade/start of rifling will determine the OAL of finished round and may vary barrel to barrel. Since case wall thickness will vary depending on headstamp (usually around .010"), adding .020" to the diameter of the bullet will either add flat taper crimp or slightly negative taper crimp shown below.

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File Type: jpg Taper-Roll Crimp1.jpg (48.2 KB, 4165 views)
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