I did a couple of more mods to the gun and got the numbers. The graph shows the temp when each test was done. My attempt at building a power adjuster was, to put it politely, an abject failure. All else seems to move in the right direction. What was very interesting was that after I got done with the last test in .22, I installed a 16" .177 barrel. I was expecting to see velocities way up in the 700's but actually saw the velocity drop into the mid-630 FPS range. This particular barrel only has a 1/8" diameter barrel transfer port hole so I'm guessing that this is simply a choke point. The RSD's when using this barrel were also extremely low (0.5% over a 10 shot group) so that lends a little creedence to the small transfer port hole acting as a regulator, albeit one that doesn't allow much in the way of flow.
It is also no surprise that doing these mods is blowing more and more CO2 out of the barrel. I'm probably contributing more to global warming by doing these tests than most of the third world and I'm sure I'm leaving a carbon footprint that has to be Sasquatch-esque. While I didn't show it here, the final test I did was with a much stonger hammer spring and that got me to 670 FPS on the 24 " barrel at 63F. However, it looks like I was only able to get 12 good shots out of a cart before the velocity started to drop like a stone in the ocean. About the only thing left is to wait until the weather here in Pittsburgh warms up so I can see what happens at higher temps.
Here are the mods and the order in which they were done.
Test 1 is stock valve and springs and running off carts. Barrel and valve milled to seat poly tube transfer port. All tests will use Daisy P-Max WC pellets. Standard bolt.
Test 2 adds extended probe bolt.
Test 3 opens exhaust port on valve and barrel xfer port to 11/64" the ID of the poly tube
Test 4 angles valve exhaust port
Test 5 adds a crude power adjuster = about 1/8" shim behind hammer spring
Test 6 removes crude power adjuster and adds weaker valve spring. Same # of turns, wire dia at .0.35" vs.0.044" stock
Test 7 removes 1/2 of the threads on the valve front
Test 8 re-shapes valve stem in exhaust port area