The .45 ACP does not seem to care much about case length. I gave up measuring cases, even on range pick-up brass, long ago. For defensive training and practice, the ammo is fine. A bullseye competitor might think differently about the matter.
The case length gauge measures overall case length, which in a cartridge that headspaces on the case mouth, like the .45, also means you are indirectly measuring headspace. But you have to know the headspace measurement of you pistol before the case length means anything.
For maximum accuracy, you should use a matched set of cases, all fired the same number of times, trimmed to the same length, and re-trimmed at appropriate intervals as determined by the case length gauge.
[This message has been edited by KLN (edited 07-22-2001).]
When I was tooling up for my Dillon 550B, I bought the case gauge. Therein began my troubles. Some of my rounds were too tight to go easily in/out of the gauge, so adjustments were made to taper crimp die so they would. Big mistake. now my rounds wouldnt even headspace on the case mouth,(they were going too deep in chamber), Failures to fire, (primers too far forward in chamber to be ignighted), and hellish extraction of dud rounds stuck in chamber/rifling. It seems that the case gauges are manufactured to Minumum SAMMI specs, and Colts and Glocks are considerably looser in specs, (to be combat reliable).
Solution? Threw the case gauge out in the alley, started using my barrels as gauges and problems disappeared, reliability reappeared!
Another thing, dont taper crimp your 45's unless you absolutly have too, Minumum belling of the case mouth, seat your bullets, (A few), measure the OAL and record, then cycle them thru your pistol by hand, (vigerously), then recheck your OAL. If any of them come out shorter, you may need minumum taper crimp, so bullet set back does not occur, which could raise pressures.
"Always place your clothes and weapons where you can find them in the dark"