Short case lenght 9mm & 40 SW

Yes. You only want to measure after sizing, as that narrows the brass, squeezing it out longer. It is common for load books to give the SAAMI drawing spec which is maximum case length. In the SAAMI drawings (links below) there is also a minus a tolerance. The trim-to length is then usually set inbetween the two.

Here's the thing, though: Many self-loading pistol chambers have a slight taper, even when the cartridge has fairly straight sides. When the rounds are loaded to pressures too low to stick the brass to the chamber wall, the brass moves to the rear of the chamber like a small piston and blows out sideways to fill the taper, making them fatter and shorter than they started out. Resizing doesn't restore the length 100% because it also massages some of the brass to the rear. I once tracked some .45 Auto brass through 50 reloadings (light target loads), and found it lost an average of half a thousandth in length per load cycle, ending up 0.025" shorter at the end when I finally retired what was left of it (started with 1000 pieces and lost about half of it to the range gods and, toward the end, to neck splits). None of that prevented it from working. It just couldn't reach a crimp groove anymore in the length I needed to load it to for best accuracy, so I had to taper crimp it into the lead a little.

SAAMI case lengths:

9 mm 0.744"-0.754". Trim-to length 0.749".
10 mm 0.840"-0.850". Trim-to length 0.845"

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Nick

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