From what I've learned in running my BME, you want to go with the lawn-boy type(mineral based) oils for at least 5 gallons. That will give everything a chance to wear in, and seat nicely. It's true that mineral based oils are not near as smooth as synthetics, which for break-in you want a bit more friction so it does break-in.
You might want to check my info out here, but you shouldn't run synthetic until you have 5 to 10 gallons through it. If you run synthetic from the start, it's going to take a coons age to break-in. I'm switching to synthetic at 5 gallons. I actually thought too that it would take me forever to get 5 gallons ran through it. I've got a gallon and a half to go, and I know I can go through at least a gallon this weekend. Once you get the engine in an airframe it won't take long. I ran the first gallon on the test stand, after that there was absolutely no need to continue to run the engine. It was totally ready, and I think I could've mounted it after a half gallon, and some would've said to mount it immediately. hehe..one gallon was sufficient though to fly.