[Deathfox]

there is a major air leak. And the air leak seems to get worse with the higher of a spring you are using.... Hop-up is a reasonable assumption, i would say it is mostly the bucking. Some air nozzles wont seal properly and like different angles. Look at the new and old bucking and compare them and see if the angles are different
But other places like the cylinder head, piston head (o-ring) and air- nozzle can get leaks after a short while too. Teflon tape around the cylinder head, and stretching out the o-ring on the piston head will help a lot