I have always had trouble with grease guns. They will get air locked, I suppose, and not pump. I have tried pulling the loading handle back and forth several times. When loading loose grease I try to push it down into the gun so as not to have air pockets. This has been the case for several grease guns, new and used. I wanted a gun that had the pistol grip handle and a flexible hose so I can use it one handed with the other handle holding the hose firmly on the grease fitting. I also started using cartridge refills. Worked fine. Then recently the gun did not work. Part of the cartridge had been used and I dumped the rest to put a new cartridge in. The gun still wouldn't work. Finally I thought, after examining the gun, that the plunger was not making pressure on the grease and there fore not forcing the grease into a slot in front of the piston that forces the grease out the hose. I thought the plunger may have hung up on the lip of the cartridge and it was not able to move enough to provide pressure. After a little rotating the charging handle and tapping the gun, I got it to work. Hope it keeps working and if not I can make it work again.
KEH