Choosing bullets and crimping them.
The 1st thing you should look at is a fire formed case. Here's that 2/1000th's thing again. What you want to do is take 7 or 8 fire formed cases and measure the inside/hole of the fired case.
EXAMPLE: Measured several 9mm cases and the fire formed cases measured .360"/ I could fit a .360" bullet inside the fire formed cases.
Subtract 2/1000th's for the measurement you get from the average from cases of mixed brass. That tells you the maximum diameter of bullet you can use in that firearm.
Selecting a bullet style/desigh depends largly on the bbl's of your firearms. MFG's have been cutting a step in the bbl making process to save $$$. A picture of an bbl that was not throated from the factory, note the small length of angle/sharp angle of the lands.
Same bbl but it have had a throating reamer used on it. This is how the MFG's save money buy omitting a simple step in the bbl making process.
Note that the ferrbore is longer in the throated bbl (freebore ='s length from the end of the chamber to the start of the angle cut of the lands). The angle cut on the lands is also longer/softer angle.
BBL's with no throats tend to do better with fn & rn bullets. That tight small freebore length and abrupt angle of the bbl that's not throated makes it harder to reload swc's, coated, plated bullets. The oal's are a lot shorter with those types of bullets. BBL's that have throats can shoot anything.
The chamber/freebore/throat on my nm 1911 9mm bbl from the factory.
Some people crimp, others do not. Myself, I crimp everything. I put a 2/1000th's to 3/1000th's crimp on anything I taper crimp. Doesn't matter if it's a 9mm, 45acp or a bullet without a cannalure with any caliber. It's my belief that a taper crimp on semi-auto reloads aids in the feeding of the rounds. And it also helps with consistent ignition & consistency ='s accuracy. Range brass can be different thicknesses, some have more spring back then others, length, ETC. All this affects neck tension/force used to expand the case to seal the chamber & release the bullet.
I also seat in 1 stage and crimp in another stage when I use a taper crimp. Doing this gives me a more consistent oal.
I'm sure you've seen this before.
What I DO NOT DO is set my oal's flush with the hood of the bbl's. Most reloaders see the "BEST ACCURACY" in the picture and they set their oal's at that MAX length. If you measure 15 or 20 of your reloads you'll see that the oal's will very +/- 5/1000th's if your good closer to 10/1000th's is extremely common.
I set my oal's so the base of the reload sits 10/1000th's below the hood of the bbl. Remember the setting up the sizing die so the sized case sits 10/1000th's below the hood of the bbl. Bullets will very in oal, measure some that you have laying around. If they very 5/1000th's in their oal your reload will very 5/1000th's in oal at best/if your perfect with your setup. The other thing is with extended range sessions gunk/fouling can and will build-up in the chamber/freebore/throat of your bbl's. Setting your oal's to 10/1000th's under max (flush with hood in picture above) will give you a buffer for the difference in the bullets oal's, reload variance oal's & fouling in the bbl.
Anyway just something to think about. It all starts with your bbl's & how they were made. Once you've identified what your max bullet diameters are and throat types in your bbl's. You can choose the different bullets you want to try/use. Once you have chosen the bullets you want to use you can choose the correct expander for the bullet size/coating.
Myself, I use/shoot nothing but throated bbl's in my semi-auto's. I adjust my sizing dies so the sized case sits 10/1000th's of an inch below the hood of the bbl. I use the max bullet diameter that I learned from measuring the fire formed cases. I set my oal's to 10/1000th's" below max. What this does is the case aids in alligning the bullet to the bore, the freebore alligns the bullet to the bore, the throat/lands align the bullet to the bore. The case has minimum expansion which makes it seal the chamber quicker/more evenly/consistently. All that add's up to accuracy.
Take your time and measure/study/think about what you're doing. At the end of the day it costs the same to pull the handle to make ammo that hits dirt clods at 10 paces or shoots bugholes @ 50ft. There's a lot of excellent reloaders on this website. If you take pictures and ask, I'm sure you'll get different perspectives/answers to the same question.