Looks interesting but never heard of it before accidently stumbling across this article.
Not sure about this though, my Colt 6920 is/was damn near identical to an M4 except for being semi auto:
"In the ASP’s inception, Extreme Shock designed the bullet to function the Colt M4 battle rifle at subsonic velocities in full automatic.
However, due to it’s popularity, shooters was using the round in various weapon platforms. However, there is a quite a difference in the military M4 as opposed to commercially marketed AR-15 series of rifles. The military M4 chamber is larger than the commercial ARs"