For a firmer texture with a very smooth texture, I find it best to use a large food processor for the grind.
1. Grind per usual with a medium plate.
2. Chill meat to fridge temps.
3. Prepare a pitcher of ice water.
4. Setup your food processor.
5. Process the meat in the food processor using the ice water to keep the meat from chunking up. It should turn into a kind of paste.
6. Stuff the paste into the casings.
Another good tip is to use some soy protein to help with binding. That will also help your texture out.
What kind of sausage are you making?
If you don't have this: http://www.amazon.com/Great-Sausage-Recipes-Meat-Curing/dp/0025668609/ref=pd_bxgy_b_img_c