Wow you are doing it the hard way with a hand grinder. I cut a reasonable amount of the silver skin out I also add pork fat and some slab bacon to my ground meat, I like the way it tastes. When I run meat through the grider I grind it twice once on a large size and then smaller, plus that makes sure everything including the added fat is mixed well.
I use my dads smaller grinder which is a pain since everything has to be in 1" cubes to fit and I need to go slow otherwise it will clog up the grinder. My cousin has an industrial grinder that he got from a retired butcher that will darn need take a whole roast and grind it without missing a beat. After using an electic grinder I will never use a manual one just too much work. I am now on the look out for an industrial/commercial grinder.