I read an article once, a very long time ago, by Colt engineers. They said it was designed to address a very, very rare situation involving full auto only, and a specific round, and a specific magazine. Apparently when fired on full auto with that round and that magazine, the "next" round in the magazine tended to bounce or rattle around a little bit and could stub up without a ramp. They said it would never, ever occur on semi, even as fast as you could possibly pull the trigger.

I don't know. Just passing on what I remember reading.

P.S. I think the round had a very high rate of fire that was far beyond what the current recomended rounds were finally toned down to.