Yep, that was the correct answer. 9mm brass tends to get shorter over time as its reloaded. You can trim it if you want, but about the only end would be to get uniform bullet seating. Might be more time effective to just sort the stuff you've got by length, then reload it in batches by case length.

It might also depend on the kind of shooter you are. If you buy once fired, or God knows how many times fired, sorting or trimming might be for you.

But if you buy your ammo new and generate your own once fired brass, you can be pretty darn sure its the same length if you keep it together.

I've lowered myself to the bottom of the barrel and purchased gun show bags or 1000 empties. It was for a reloading project back about 1994. I'm a skeptic, and the stuff I paid a premium for that was labeled as once fired may or may not have been. It did look nicer. I didn't bother to check lengths or trim it. I used a single stage press to load it. You can see or feel a difference in length if you concentrate. I couldn't tell.

And it shoots just fine...still. My youngest son hit the stash pretty hard a couple of years ago. He never complained about it (and your own sons would complain even about free ammo.)

So my take on it is you've hit upon a non-issue. You can pursue it as much as you want, it will burn valuable time.

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Dick Burg