I hate peel washers! I hate peel washers!
Now that I got that off my chest, the peel washer is a set of very thin washers glued together to a certain thickness.
When you install the FSC556 it will (most likely) not stop in the correct position; i.e., flat with logo at twelve o'clock.
Get it as tight as you can with your two fists. Then you have to estimate how many degrees you are from having the flat with logo at 12 o'clock.
You will be able to use a wrench and get about 5 degrees or so more than you can by hand.
Each laminate (thin washer layer) is worth about 10 degrees of turn. Get an exacto knife, or similar very thin blade. Remove the FSC556 and the peel washer from the barrel.
Heat the peel washer with a heat gun, cigarette lighter, propane torch, whatever and use the knife blade to remove a thin layer (washer) from the peel washer. These will be almost paper thin. If you are 10 degrees off, that should do it. If you are off more than 10 degrees, remove the appropriate number of peels.
Put the peel washer back on the barrel and re-install the FSC556 and see if you are really close to the correct location. If yes, use a wrench for the final 2 to 5 degrees and you are done. If not, do it again.
Nice thing is that if you take off too many, just take off another to bring it around again.
You might try using the bird cage washer in combination with the peel washer. Proper "clocking" of the FSC556 is very important to its' proper function.
Photo below does not really show the flats, but shows the side cuts that do the compensation.
I screwed with mine for an hour to get it just right, but I am pretty retentive.
Good luck, and I hope this helped.