Originally Posted by hyarbour
The biggest problem usually turns out to be air in the grease. Just a little bubble in the tube getting up unto the pump cylinder screws them up. Try taking the tip off the gun and pumping it a few times to try clearing it.
Maybe I've just been lucky, but I've never had any of these problems. I have a variety of grease guns, US and foreign made, pump and air-powered, and all work fine with no issues. There really isn't a lot of technology to it.