Free: Contests & Raffles.
Try chamberring your brass without bumping it back. If it chambers easily you don't need to bump it, wait until it is snug to chamber and them bump it just enough to chamber easily.
It sounds like you have a a chamber with tight tolerances, which is good as you won't be overworking your brass when you resize. If you are loading for a hunting rifle I would recommend that you do a full length resize after each firing. Set the die up per the mfg instructions and size away...in my experience this gives 2 to 3 thou set back. In reloading consistency is king.
Trimming is really about how uniform you want to make ever batch of reloads. If you are within spec of the manual trim max length you will be fine for safety reasons but if your looking for ultimate consistency say every 2 reloads you trim to shortest case length granted as long as that length is writhing the max trim to length you can in your mind say that group wasn't affected by my trim to length. I would say it's all about what you as a reloader are trying to accomplish. Some guys want to know every thing is consistent from every reload every time to cut down on those groups they are shooting. We are talking .1 of an inch maybe smaller. It's hard to say what you personally are trying to get done. I know in my 300 wm I have to prep the cases and spend more time on that process because it seems that if I slack on that groups open up. On my 6.5x47 lapua I can get away with only making sure everything is within the book specs and not worry about it. That gun will shoot with a rock as a bullet it seems. But to better answer your question after all that nonsense in my opinion I would trim to the shortest case length when you trim provided it is within spec and not all the way to the book minimum to cut down on trimming the case more then I have to but ymmv