As far as I can tell, there is no specific definition of tallow. I see nothing that says it has to be organ fat. By all dictionaries I see, tallow is rendered animal fat, nothing more, nothing less.
It absolutely can be used unaltered for muzzleloader purposes. Different animal fats have different properties though. Bear fat is going to be the most well known, or talked about. At room temperature it is grease like consistency. Above 80ish it will melt into an oil. Below about 60 it turns solid, but the good thing I've found is it does not get any harder than that, at least down to -10. The problem with lubes that include beeswax or other stuff, they become frozen. Tallow doesn't do that.
I use rendered bear fat, AKA bear grease, unaltered for all muzzleloading purposes. I use it on patches, wads, and for any gun oil. I don't say it's all rainbows and unicorns, but it works. It's right up there as one of the best patch lubes I know of, and it seems to work just fine as a metal protectant.
Pro tip: Like many, I was stuck in the old way of rendering fat, the way I'm sure almost everyone did it. Cut into small cubes, then heat slowly until it was all melted. Often I used a crock pot. Well it turns out that is not the best way at all. Instead cut into generous sized cubed, don't waste time. Then run once through a meat grinder with a coarse plate. Add a little bit of water to the bottom of whatever you are using to heat, and then add the fat. Before it might take many hours, I've even had to go a whole day to fully render fat in crock pot. The grinding method is just tops. I rendered about 30 pounds of bear fat in about an hour and a half. The water really gets things going quick, then boils off in time. The grinded up fat melt super fast, it will melt in your fingers. One last tip, stick the fat in a freezer before you cut it. 1/2 frozen fat practically cuts itself.
