I'm still confused by your statement that the range brass "seems a bit loose" in your chamber. Perhaps that needs further explanation.
If you want to know just how much the range brass might be undersized for use in YOUR chamber, partially seat some spent primers so they are quite proud and chamber them. The protrusion of the primer will show you how much short they might be. Or you can use a headspace comparator gage to measure base to datum and compare to your fire formed brass.
I presume you're not talking about a belted cartridge.
If you want to know just how much the range brass might be undersized for use in YOUR chamber, partially seat some spent primers so they are quite proud and chamber them. The protrusion of the primer will show you how much short they might be. Or you can use a headspace comparator gage to measure base to datum and compare to your fire formed brass.
I presume you're not talking about a belted cartridge.









