My 504 serial number is also in the 30xx range. It will shoot 3/8" groups (and a few better) at 50 yards with RWS 50.
I got mine at a salvage company, after they bought out a gunshop's inventory. I spied it in the rack from across the counter and noticed the beautiful woodgrain.
There are pictures and description of my accurizing process on RimfireCentral.com "Tips and Tricks Forum".
People are like rifles. Some are tried and true, having great eyes, personality, and fun to be with. Others never seem to hit the mark with you. Still others go off half-cocked. Still, it's nice to know most of them.