Hey, Bart,
Can't help with the B40, but here's some numbers for the 350. The bottom block of data is the numbers I got when I first got the gun. It was a warm sunny day, and the gun was sitting out in the sun. The top two blocks were shot a week or two later, same temp, but overcast. That's the only explanation I can come up with for the decrease in velocity after a fair amount of shooting. Hope this helps with whatever you're working on.
Dave