Years and years ago, in a land far, far away with a name that no longer exists, two bored G.I.'s with access to a somewhat less than secure arms room containing a few M16's that were "mavericks" (that's a weapon not on the unit's property books), and a hacksaw, whacked the barrel off one of the mavericks just forward of the front sight. And, installed it on a CAR-15 lower, just to see what would happen. The contraption ran like a sewing machine. I suppose if we'd had easy access to a machine shop, we might have threaded the barrel for a flash suppressor, but we didn't think about that until later.
Couple-three caveats to the story.
It was a relatively warm climate some might describe as "sweltering".
I have no firm recollection whether the CAR-15 we used as a donor for the lower was an E1 or an E2. Don't think I knew the difference in those days.
And that's an unsubstantiated example of one. Another result may vary.