I seem to recall the barrel stamping on my M-16 during my days in uniform saying it had a 1 in 7 rifling twist.
I seem to recall the civilian version saying it had a 1 in 9 twist.
But as I know zip about the M-4 and it's civilian version...
(But, I also seem to recall my memory going flaky on me lately! Woohoo!)
The military bullet weight was increased some time ago, and the twist changed too. This stuff is Squantos' profession, so I expect your solid answer soon.
Don't worry about the memory thing....Muttly has Memory Flakes too...and look how great he turned out anyway!