1. SETTING UP: For 6 lbs. of sausage, you'll need a cleaver; 5 lbs. venison stew meat, cleaned of silverskin; 1 1/4 lbs. chopped pork; 1 lb. fatback; meat grinder with sausage-stuffing nozzle attached; 1/4" natural casings (in grocery meat departments) soaked in cold water for 1 hour; salt and pepper.
2. CHOPPING INGREDIENTS: Working in small batches and using a very sharp cleaver, chop the venison, fatback, and pork (if not pre-ground) into 1/4" chunks. Combine chopped venison, pork, and fatback. Season meat and fat mixture to taste with salt and pepper.
3. FILLING CASINGS: Secure machine on counter. Cut casings into 3' pieces. Gather casing over nozzle, bunching it up on nozzle until only 3" remain at the end. Crank mixture evenly through machine to fill casing, easing filled casing off nozzle as you go. (Filled casings should be as firm as medium-rare meat.)
4. TWISTING LINKS: Pinch filled casing to make links 5" long. Twist at pinch—right hand toward you, left hand away from you—to form links. Prick sausages several times with a pin to release pressure. Refrigerate 1 hour, uncovered, before cooking.