firerescue220 all great info above. I will add that using a 1/2" or 12.7mm outer diameter tube, you may find that your sausage mix is very hard to stuff thru that small size, especially if you are using a grinder to stuff. With a grinder, you may find it is just churning the meat in there until you put pressure on top to force it out thru the tube… I did. 32mm sausage was ok, but 19mm was impossible with 1 person and a 1hp #22 grinder. That is the event that convinced me to buy a stuffer 
Here are some tips to help make it possible to stuff the small casings. With a good stuffer not all these are needed, but these tips will make it easier for you:
- You can use more water, and will need to. I used a full 24% water on my last venison beef batch, and they were great. On a recent podcast, jonathon said it was required to use 1.5L in 25lb batch with new elec 15lb stuffers, and 19mm casings on a 13mm tube. That was to make it work. That is 13.2%. An electric stuffer is like 10 times easier than using your grinder, so you can see why maybe more.
- Your goal is to ensure the mix is at maximum fluidity. That means anything that binds up the mix early is bad.
- Don’t grind and cure meat one day then stuff next, you need to stuff ASAP after grind sobit doesn’t set up.
- Don’t add cure and let it sit, this binds up the meat. Stuff immediately after mixing meat with salt, spices and cure. You can let the stuffed sticks cure overnight. If you want to smoke immediately, I recommend adding cure and then ALSO a cure accelerator so you can start cookingnthe same day. I use 1 vitamin c 1000mg tablet per 1kg meat/water. Or Walton’s sells sodium erythorbate.
- If you use a lot of water, which you often need to with small say 10mm tubes into 16mm cases, you’re going to need something to bind it. Walton’s sure gel works decent. Or instant nonfat dried milk which I like. Don’t use the carrot based super binds, it will lock it up too much. Mix until good sticky protein extraction but not too much.
- Beef and venison bith absorb more water than pork, so with high water batches use more of those two.
- The extra water will evaporate out during cooking and smoking if you keep temps down 180 to 200. If you sous vide, the water gets locked in, but you can still dry them more if desired by just leaving on tray in fridge a few days.
- Heres a mix for reference that I know was super easy to stuff and came out perfect: 1.5kg venison, 0.4kg pork fat, 0.85kg 80/20 beef, about 6 lbs total. Walton’s Willie’s snack stick seasoning 159g. 6.8g cure1. 3 vitamin c tablets, 1000mg each. 76g nonfat dry milk. 650ml water was 24%… started with less and just added until stuffable. 16mm smoke collagen casings thru 10mm tube, 3.5 hrs on traeger smoker to 142 internal then sous vide to 160.