When I was a kid we had Red Ryder BB guns, but souped them up. Out of the box, they were really weak shooters, just half-assed toys.
A couple of friends and I discovered that oil would change all that.
We would squirt motor oil down the barrel until it was oozing out all over the place, let it percolate for a while, then dry fire the gun until just a fine mist of oil came out.
The BB velocity would be at least triple what it was before supercharging. You could shoot through both sides of a tin can, where before the BB would bounce off. Sparrows, starlings, even pigeons paid the price.
I guess the oil caused some rubber seals to swell and contain air pressure better, but don't know for sure. We never tore one down to see how they work.
But I never heard of anyone shooting their eye out.
I recently bought a Gamo breakdown pellet gun, and its power and accuracy are really impressive. No more squirrels on the bird feeder.