Well it all depends on the workload as well as luck and practice. Not every two pulls are going to be the same, even if they are timed out presses of the foot switch. (IE: Hold for exactly 1.5 seconds.) Seeing how hamburger grind is a mix of fat and muscle, not every bit of it is going to be perfectly mixed as it comes out, so you'll have packets of density that also affect the weight.
I dont know what happened, thought I hit reply and sent my post. If this is a double,post, my bad. I work in the meat dept of a local grocery chain, specifically specialty cuts where we have our own meat counter with full service with select beef, pork, chicken and seafood. We also grind and do our own cuts, so all chops, steaks and etc are done by us. The machines we use for grinding is operated by a foot switch, which activates the auger to push the meat into the grind. It's rather impossible to hit a pound spot on using this machine, we know the range because we do this all day.