Tim made more than one gun with identical serial numbers if they were different model. He serialized the barrel mounting blocks rather than the receiver, so swapping from angled blocks to upright hunter typically meant a different number series (not that much attempt was made to produce the guns by model year.
As to poppet SEAT DIAMETER (the stem is the thin shaft, the valvehead is the delrin part with part guiding the return spring and the other sealing against the VALVE BODY seat face). The gun was designed at first ONLY for 20fpe field target use, and yes it was convenient to adjust power level by modifying the seat-to-valvehead overlap margin, since it was easy enough if an old gun that had remained charged for many years and had lost a little power could be restored to original power by sading the delrin seat a a few thou to bring it back to original clearance (typically they grow by settlling over a long period).
Frankly the early guns never had, nor do they need a port restrictor … yours was added later for some reason.
Now don’t believe these guns NEED smaller poppet seal diameters to shoot harder! I have a couple (still unregulated USFT’s) in .22 cal that can easily shoot well over double the 20fpe limit, and even moret, albeit they ARE modified, but the poppets are absolutely standard items with around .180+ seal dia.
The latest one Im playing with the is for long range Field Target and 100y benchrest coming up in Ashland Or. I built it 14yrs ago for 50yd BR shooting when the open class allowed 34? Fpe and it did pretty well. But now I’ve bumped it to around 50fpe in .22 with the 25.4rds. Im only getting about 30 consistent shots on a charge, Though my second gun, which holds more air, gets 50 good shots, still fairlly low preseure And. CAN shoot up t0 65fpe, but not as accurately.
So don’t sand the valve seal down, just shorten your valve return spring a little (based on you post and picture). Also, take that port restrictor screw out and grind the end flat, then put a well firring drill rod up the port and run the screw in til it touches and loctite it there.
