Help please!

I am thoroughly enjoying my entry into air pistols with my recently acquired FWB Model 65. Though the gun shot well, I noticed the breech seal had begun deteriorating, so I’ve replaced it, the nearby buffer, and the piston buffer.

Upon reassembly, and after then reading a few airgunBBS.com posts, I’m concerned with two things: the placement of the rear recoil slide’s shims, and the proper pellets to shoot.

The rear recoil slide rod was found to have 4 washer type shims (unsure if they are of the same thickness). I had not accurately noted their placement upon disassembly, so I originally reassembled the pistol with three shims to the pistol’s rear, and one shim to the pistol’s forward end (facing the Reverse Lock, 1600167.1). Though the pistol functioned, I read an account on airgunBBs.com which caused me to change the shim location, now placing three shims on the recoil slide rod’s forward location, and one shim on its rearward end. There may have been a slight reduction in felt recoil, the shim repositioning seem to have little effect. My main concerns are: how to determine the correct positioning of the shims; what is their purpose; and is the rear recoil slide rod supposed to move far enough rearward that the Reverse Lock shifts to block the recoil slide rod’s forward end from moving through the hole in the rear of the Reverse Lock?

What pellet/projectile will yield the best accuracy? When I first received the pistol, I was so anxious to try it that I used some old flat nosed pellets whose origin I can’t recall. These old pellets actually shoot better then several types of new Gamo pellets I recently purchased!

Lastly, are there any adjustments/modifications I can make to improve the pistol’s accuracy, and is it possible to date my pistol’s manufacturing date (Serial #23143)?

Many thanks in advance! Michael