My goal is simple. I don't want bullets spinning in the loaded case because of light crimps, nor do I want distorted cases because of excessive crimps.
I think we're all in "violent agreement" here... It's only been in the last few years that I've encountered such large differences in 9mm brass case length and mouth thickness - it coincided with me shooting 5-10x more pistol ammo after I retired, and began hoovering up brass wherever I could find it.
Early on, I was shooting 9mm Glocks and SIGs. I never encountered a feeding problem. I never gaged my reloaded ammo. It just worked. I had brass so old the headstamps were almost gone. I'm using '70s-vintage RCBS dies (taper crimp die) in a Dillon 550.
Then I bought a 1911-based 9mm with good sights. WHAM. I hit the wall. Every 5 rounds or so, I'd have a round jammed so tight that getting the slide open safely was a major challenge. Same thing happened with CZs purchased by myself and my son.
So I bought a case gage (again, Wilson spells it "gage"). I quickly learned that CBC-headstamped cases are almost always the shortest OAL with the thickest, hardest brass which resulted in the highest number of gage-fails - the resized case would drop right into the gage, but seating and crimping a bullet (jacketed or polymer) resulted in many over-thick rounds. I played A LOT with resizing and crimping to see if I could eliminate this brand-specific issue. Long story short, I just accept that CBC brass is going to have more rejects because the brass is thick. Every Single One of these "rejected" rounds has worked just fine in my Glocks and SIGs. Sample size is in the thousands. The reloads that pass the gage test run flawlessly in all the tighter-chambered pistols - again, sample size in thousands.
I learned that FC, Blaser, and Speer was super soft and seldom gives any trouble. GFL, Starline, most others are usually good to go. I learned that R-P case heads are subjectively "small" and cases that look the least bit beat up are going to fail the gage test so I just scrap them. Winchester cases do fine usually. Cases with military-style headstamps - I usually encounter WCC - are generally ok but the primer pocket shoulder is so sharp that seating a new primer has to be done carefully to avoid tilting/crushing the primer. PPU cases are scrapped. Period. I don't even bother with them.
My powder measure is set to bell the shortest (CBC) cases enough to allow the thicker polymer-coated bullets to seat easily. This results in a bit too much bell for longer cases, but I have yet to have a long case split at the mouth.
Crimping is set just enough to remove the bell. No more. I read someplace that, in tapered cases, it's the "shelf" created by seating the bullet into the resized case, not the crimp, that prevents the bullet from pushing into the case when it hits the feed ramp. It's important to reiterate that I spent a lot of time trying to adjust crimping to get rounds that had failed the gage test to subsequently pass. Never happened. So, the crimp is set to minimal. (Caveat: this applies to tapered cases, NOT straight-walled stuff like .357/.44 Magnum where a strong rolled crimp into the cannelure is mandatory!)
Now, some cases that have been loaded a few times and/or fired in Glocks or other firearms with huge chambers simply won't resize to factory spec because the case web (solid part of the head) expands, and it can't be resized by standard dies. Had a good discussion with Dillon about that. I encounter very, very few of these.
Hope this helps.
