I use grease where specified on my M1, and I've tried it on locking lugs on bolt guns before.

Interestingly, the component in grease that does the lubeicating is oil. The 'grease' is jut a thicker carrier to hold it where you put it 'better.'

So, I don't think the question is one of better lubrication, so long as your grease is as new in lube technology as your oil is. Rather, I think it is one of whether the lube stays put better with a thicker carrier (grease) or a thinner one (oil).