I never clean it. if i get any crusting on the outside of the case i use a small square of white sanding pad. It takes off the crap without touching the petina. 

40 Rod

critter68
The SS pins do indeed give dirty brass a good shinny cleaning. I normally shoot my 38-55 with black and duplex loads so cleaning after each firing is mandatory, IMO. Bent or distorted case mouths have not been a problem in my experience when using SS pins.
If you have been getting blow-back at the case mouth there is a cure for that. I had my Simmons re-decaper modified to bell the case mouth each time I punch out a spent primer. The expander plug is adjusted so it just kisses the case mouth as the primer is ejected by the decapping pin. That keeps the case mouths nice and round, virtually eliminating any blow-back.
The tool shown is for 32-40 but properly sized decapper plug will work the same for 38-55. If you don't have a Simmon's tool, buy an expander button as comes with reloading dies. That works also and is what I use for my 38-50 (Rem).

If you have annealed the necks they are softer and seal in the chamber preventing the blowback on the necks.

When I start seeing blackening on the outsides of my necks I know it is time re-anneal my cases.

Starline brass is delibrately made hard and must be annealed even before the first shot.

And of course I only use fired cases and never resize my brass which means it does not case harden as quickly and is a tighter fit in the chamber; again being easier to seal tight in the chamber when fired. 
So less blowback. And easier to clean.

I use the same case so I only have one case to clean at the end of the day and I clean it by hand.

JLouis

When I see a little darkening, I wipe it with brass wool.  My case fits well enough to compress air and pop back out 1/4" once in a while.  I suppose it fits about as good as it can.

Critter you would be allot better served to just use one single case. No two cases are exactly alike and more times not no two cases will provide you with the same shot placement on the target. It is not untypical when I have to change to another case to also have to re-sight in just for that specific case and at times to also alter the load slightly. One could go through all 500 hundred of your cases and carefully sort by shooting to come up with enough for a match but it is also allot of tedious work. If just wanting to shoot offhand you would probably never know the difference. But if wanting to be very competitive off the bench or doing load development using one case is the best way to go. If like you say currently working on getting the rifle to shoot and using multiple cases the poor group sizes, uncalled for shots / flyers etc. could just very simply be caused by the use of multiple cases alone. Bottom line is you will never find the answers to your why's and how comes your rifle is not shooter better or possibly not shooting very good at all. Also keep in mind for about every ten degrees in temperature change more times than it also requires a slight change in your powder charge to keep the rifle in tune / consistently shooting it's very best. This also holds very true from one day to next as density altitude, humidity etc. also change not only during the day but from day to the next. It is also best to have the extremely accurate and easy to use Harrel Schuetzen powder measure and to be loading at the bench so you can keep up with all of those changes. Very seldom I am using the same powder charge but a slight variation in tenths from the norm. either having to up and or down as is required at the time. 

JLouis

  I use multiple cases and find it a considerable advantage for accurate shooting.