OK, I am really not crazy, and I do know the difference between M4 ramps and rifle ramps. But, get this…
So, I just bought a new in wrapper, Colt 20" 1/7" gov’t profile M16A2 type barrel. Checking it over last night, I noticed the feedramps look almost like M4 ramps? Not quite as deep, down from the shoulder, but definitely cut further than rifle ramps. I am going to go ahead and use an upper receiver without ramps, just to ensure I don’t end up with a lip to catch the bullet tips. But, it really looks like I might be able to use an M4 upper receiver (wish I had an unbuilt one on hand to check).
Yes, I coined the term “M2” feedramps to get everyones attention, but in this case, it has some merit, maybe. 
Anyone else seen this on Colt rifle (not carbine) barrels?
I know, I need to post pics…I will, but can’t right now. Maybe tonight.