Mini Grease Gun Advice

I bought one of the cheap mini grease guns, and in my first attempt at re-greasing the axle I had a lot of trouble actually getting the job done. I did eventually get it done, but it seemed like it was getting air pockets in the gun on a regular basis and every 5 or so strokes I had to take the cartridge out and repack it to get it to work again. A quick search around the internet tells me that I am not alone on this boat trailer forum:

http://continuouswave.com/ubb/Forum3/HTML/014084.html

So before I ditch this mini gun for a full size gun, does anyone have any advice for how to get it to work better, or if there is a setup issue? I expected it to take more force to squeeze the pistol grip handle, but the problem seemed unrelated to that, as if the plunger wasn't capable of pushing the grease back into the piston (or does it work some other way?).

Maybe I was just too cheap and I should have bought a brand name gun from Lincoln or Alemite? Any ideas?

As an aside, the dark lithium grease made it difficult to tell when the old stuff was finished and the new stuff was coming out...

I have found mini grease guns to be more trouble than anything. If when working correctly you are always changing cartridges. A good quality full-size gun is a better all around choice for me.