So you want to process military brass? Here's how:
You will need a case gauge to do this properly. The first thing to do is inspect your brass for any unusable pieces. Dented case necks and small dents in the body of the case don't render the brass unsuitable for reloading. If the case has a dented case neck, take a round punch with a tapered neck and insert it into the case and lightly tap it with a hammer to get the neck round again. It doesn't have to be perfect because the expander ball in your resizing die will get it perfect. Once the cases are sorted you will need to resize and deprime the brass.
If you are doing this on a progressive press, you will need to ensure that all the stations have brass in them. If you don't do that when setting up your resizing die, you will get false results because the tool head responds differently with only one case in the machine.
Make sure you are using plenty of case lube when resizing military brass. Without a case in the resizing station, run your resizing die down to the shellplate and then back it off a couple turns. Then insert your test case into your press and run it down. Remove the case and check it in your case guage. It probably won't fit. Turn the resizing die down 1/4 turn and try again. Keep doing this until your case fits into the case gauge completely. Now lock your resizing die down. No need to overdo it. Once the case fits in the gauge you are good. If you have a specific rifle that you are loading for you can also do this check in the rifle chamber.
Once the shoulder has been properly set back, you will need to trim the cases to length. Consult your reloading manual for the proper trim to length for your caliber. You will also need to ream or swage the primer pocket. Once this is complete your brass should be ready to reload. Please remember to be safe with your reloading and always start with the lowest powder charge recommended and work your way up verifying your velocity with a chronograph.