Looking a gift horse in the mouth…

I just got my tank back from Tony, and have been able to shoot my SS a bit the last couple of days. It is consistent and accurate, and LOVES the Beeman FTS pellets. It shoots one ragged hole groups at 20 yards, and at 40 yards, most of the holes are touching. It it truly an accurate gun, and will easily put down any squirrel, crow, starling, rabbit, or sparrow I decide to shoot with it, especially if a headshot presents itself. However, there is one thing that bothers me, and I know I am being petty about it, with the gun being as accurate as it is. It shoots at a maximum velocity of about 780 fps with the Beemans. Now, I know that it plenty fast for the aforementioned shooting purposes, and that as accurate as it is, it will make up for a somewhat lower velocity. It doesn’t bug me so much that it shoots about 50 to 70 fps less than what other people have mentioned getting, as it does that I can’t figure out WHY. I have done the following things, but to no avail:
-Cranked the power wheel – just made it louder
-Polished the inside of the body
-Adjusted the top hat
-Added two 1/8th of an inch bronze washers behind the original hammer to add weight, and gained about 12 fps over the stock hammer
-Used a 2 inch by 1/8th inch thick by one inch OD bronze thrust bearing as a hammer, and gained 16 fps over the stock hammer
-Had Tony do a valve job after I destroyed my valve collar trying to get it off to tune the valve
-Changed the breech o-rings – twice
-Polished the sear, in case it was rubbing on the hammer during firing
-It is lubed with a spray on dry silicone lubricant, like so many others here use
Is there something glaringly obvious that I am missing here? Is it possible that I just have a stiffer valve spring than some others, and it just isn’t staying open as long? Usually I can figure these things out, but I am stumped.
Thanks,
Chris
–