270Man, if you decide to sit down and do some serious measuring of straight wall semi auto pistol cases, you're going to get an ugly surprise.
You'll discover that most are shorter than the length specified.
I one measured 1,000 9mm cases, and never found one that was as long as specified. I've gotten smarter (a little) as I've gotten older, and I no longer do that kind of repetitive drudge work, but I haven't found any 45 ACP cases that were specified length, either.
In practice, I think 9's and 45's are held by the extractor, or the bullet touching the leade. They sure aren't headspacing on the case mouth.
Measure your chamber, and some cases- you'll see what I mean.
I must say, whatever the cases headspace on, they all seem to work.