Use a dark Sharpie marker on the shoulder & the junctions of body & neck as well as around the base at the pressure ring. Hell... color the whole case. Chamber, extract, & look for marks where it's hitting.
See above comments for remedy.
If the base needs sizing, I've heard that stripping a 45ACP sizing die will allow you push the case all the way thru. Carbide will be easier. Not sure if I'd do this to a loaded round..
I just used a sharpie marker and painted the entire case and kind of what I suspected the problem is on the shoulder of the case. My COAL is good, base of case is good, I saw contact markers on the shoulder of case. Is there any way I can bump that down with my die? I thought when FL sized my case that it was automatically bumping the shoulder back. As another amp fire member said I may just have to buy brand new brass. Or I may be able to fire this stuff through my chamber to get it to fireform to my chamber and continue to use it.