My only pellet gun is a 46 year old Sheridan Blue Streak in 5mm[.20 cal] it shoots 14.3 grain Sheridan cylindrical "Penetrator" pellets with great accuracy and, it is deadly! I think Benjamin bought them out and still makes them.
I know there are much more technically advanced air guns these days and I might consider getting a new hi tech something, BUT, I've killed a nation of squirrels,crows,snakes[including a 6'3" Diamondback] fat 'coons, ferrel cats out the wazoo, and one 30-35 pound[estimated] gray fox.I have no idea how many pellets have gone down the barrel [always at a max. of 10 pumps] but, they surely are in the tens of thousand,maybe 20-30 thousand.
I have never had a problem with ANY maintenance on this superb piece of plunder. Not even a new "o" ring on the "bolt"! I lube it every 3-4 months with Crossman"Pellgun Oil" and according to the directions, I leave it unloaded with 1-2 pumps[I've always used 2] ready for the next "call to duty".I can't say enough about the quality, accuracy,and reliability of old "Huffer" Nick