Unless you're a master at timing your burgers, you need to add fat. I add varying amounts of other meat/fat for different purposes, but as an all purpose grind I shoot for about 70% Elk, 20% Pork fat back, and 10% pork shoulder. Cook somebody a burger of that and they'll be floored...you don't have to tell them there's a bit of pork in it! If you go this route, get pastured pork products, not costco stuff. Factory farmed pigs and pastured pigs might as well be different animals from a flavor perspective.
Don't add pre-ground meat, and don't add bread crumbs or egg; it's totally unnecessary. If your burgers are falling apart, there are a few culprits:
1) your patties are too warm - just make sure they're well chilled before hitting the grill.
2) your grill isn't hot enough.
3) your fat got too warm during grinding and started to coat the proteins in the meat - once you've got your chunks cut to the appropriate size, put them (pre-blended) back on a sheet tray and stick them in a freezer until they're about 1/3 frozen....this will help the cutting blade slice instead of smoosh the meat. work in batches to avoid getting things too warm.
4) you're adding too much water to the blend (if you're adding soy sauce or mustard whatever prior to shaping the patties).
If you like beef suet more than pork, go for it, but make sure you add some fat.
100% lean meat is crime against flavor. If I had served that in restaurants back in the day people would have walked out.
