I am getting pretty frustrated using hand pump grease guns. Just when you get under a machine to grease some difficult to reach fitting the gun looses its prime and you gotta pull the plunger back, unscrew the cap and smear a big gob of grease from another cartridge into the small void that caused the gun not to pump anymore. Am I doing something wrong in the loading of the cartridges or in using the gun? I've tried different brands of grease and even bought a new Lincoln grease gun, but the problem crops up on almost every cartridge I use. Is this just how these grease guns work or can I do something different to prevent this from happening. Thanks for your advice.