Is gun oil food grade?
I've always used some type of cooking oil.
Cooking oil I guarantee you will gunk up and cause more problems than it solves.
Personally, I wouldn't go spraying gun oil on my sandwich...but I'm guessing if I did, it would take a lot of sandwiches to kill me, and in the case of the BC, I only use it on the portion of the shaft that spends its life sitting in the sleeve. Not like you're lubing the rollers or anything.
As I mentioned, I used some other type of grease originally...it was like six years ago so I'm not sure what, but I think some automotive grease I had laying around. I can tell you when I first tried the gun oil, after I reassembled and did a test crush, it felt a little different than it ever had. Very scientific..."it felt a little different". Was just the smoothest / easiest it had ever crushed anything though.