I prefer the natural hog casings. A little more work but it makes a better sausage. Here's my Italian sausage I make.
Italian Sausage #4
6.5 pounds boneless pork butt
1 pound fresh pork fat
6 Tablespoons cracked fennel seed
1 ½ tsp garlic powder
1 ½ tsp onion powder
1 tsp paprika
1 tsp parsley
2 Tablespoon kosher salt
1 1/3 Tablespoon freshly ground black pepper
In a large bowl, toss together thoroughly the pork butt, fatback, fennel, spices, cover with plastic wrap, and leave refrigerated for 1 hour. Grind through medium plate and stuff into pork casings. Refrigerate, loosely covered, for 12 hours before cooking or freezing. Product must be cooked before serving.