Welcome to SMF!
If you're using natural casings packed in salt....
Try initially soaking the casing in warm water for about 30 minutes , then flush them out.
Soak overnight in the fridge in water with lemon juice added (1 teaspoon lemon juice per cup of water)
Change to warm water (helps with casing expansion) before stuffing and do not under-stuff, you want maximum expansion of the casing.
I would stuff immediately after grinding/mixing so that the mix doesn't begin to set-up....again, so that you get maximum expansion of the casing.
Take special care when cooking, too high of a temp, especially initially, can make casings tough.
HTH
~Martin