Cut up the chuck roast and pork butt into cubes small enough to fit down your grinder.
Place the cubed meat into a large container, add seasoning, and mix it in by hand.
Place meat into the grinder’s hopper and pass it through a coarse grind twice (using a 4.5mm plate on the last grind). Afterward, place ground meat in the fridge.
Place the casings in a bowl of warm water, separate them with your hands, then let them sit until you start stuffing.
Load the ground meat into your mixer, pushing it to the bottom. Add the non-fat dry milk and the cure/water mixture before mixing the meat for seven and a half minutes. Slowly sprinkle the encapsulated citric acid over the top at the end while it mixes for another 30 seconds. Do not overmix.
Remove the meat from the mixer and place it in the fridge while you preheat your smoker to 120°F.
Pack your sausage stuffer canister tight. Rub some fat on the silicone O-ring before turning it to ¾. Stuff the sausage into the casing placed on the horn. Leave about 2 " of room and secure the end with the ring and pliers.
Place the hanging rods on your smoker’s top rack. Tie a knot in a string attached to the sausage, hook it on, and place the hooks on the hanging rods.
Thread the internal temperature probes down the center of a sausage on either side. Set the timer for 30 minutes to let the sausages dry out before smoking.
Fill a pan ¾ full with hickory sawdust mixed with a cup of water. Mix by hand and make a well in the middle before placing the pan down the bottom of the smoker. Add a little water to your smoker’s drip pan.
Turn the smoker to 150°F, and set the timer for two hours. Increase the temperature to 175°F and set another timer for two hours. Remove the sawdust pan, increase the temperature to 180°F, and wait until the sausages reach an internal temp of 150-155°F (about another two hours).
Remove the probes and place the sausages in a large container filled with ice water. Place a wire rack on top to keep them submerged and leave them for 15 to 20 minutes.
Towel dry them off and hang them back in the turned-off smoker at room temperature for about another two hours.
Place them on a wire rack in the fridge for 24 hours before slicing, serving, and storing.