If you purchase a gun straight from the factory into the UK Via the importers wharehouse then you willbe amased at just how much muck there is in the barrel to start with.Best thing is to clean the barrel thoroughly before putting a pellet through it.After that choose a pellet and stick to it,the same pellets are better at keeping the barrel conditioned than chopping and changing brands all the time.Try and use the top quality ammo from the outset as this will pay dividends in accuracy, and stop all those nightmare sessions