Oiling pneumatic air guns

Again, no experience with a pumper or PCP type. My comment was made based on the simple physics of what is happening. When air, or any gas for that matter is compressed it heats up, That is why scuba tanks may be immersed in water while charging or the compressors have cooling fins or water jackets to keep them from overheating. Conversely when any compressed gas expands it cools, usually rather rapidly. Personally in the guns you mention, I would think any heat would be residual heat from pumping your pumper, not in a PCP as that would have already dissapited. When you fire one of those guns you are in mode where the gas is expanding and therefore cooling, simple physics.
 
20210923_103612.1632415216.jpg
20210923_102950.1632415217.jpg
But what about pneumatic pump guns? 

I think it comes down to the pressure of the specific gun. I would go with the factory recommendations for oil or synthetic base. 
For instance my crosman 2100 is a pumper but the instruction manual said I should use the crosman silicone oil for that gun RMCOIL. My 760 and P1377 both say to use pelgun oil (a petroleum product). 


I just wanted to point out that just because it is a pumper doesn't mean that petroleum based oil is safe to use. It should be fine for a 1377 however.



The top image is from the Crosman (not Benjamin) 1377 manual and the second image is from the 2100 manual. Note the caps on DO NOT use petroleum distillate