Hello!
I think the pouch was originally intended to be used (also) as a pistol magazine pouch, but actually never used in the field to store the Beretta magazine.
Here is a piece of paper I found inside the pouch of my XM9 (already posted in the forum).
http://img230.imageshack.us/img230/5462/53515101.jpg

http://img809.imageshack.us/img809/6...smcbuck033.jpg

http://img859.imageshack.us/img859/3...smcbuck031.jpg

Maybe its just a matter of semantics, but the pouch was designed and intended to be for a Beretta pistol magazine. It appears that it was never actually used for this purpose, but that was its intended use. That's straight from Mickey Finn's mouth to my ears.

Thanks Bill for setting the record straight. Perhaps what I was thinking is the "magazine pouch" was seldom utilized for this purpose. Since the vast majority of M9 bayonets were issued to soldiers whom did not carry a pistol in the field, this would seem to be the case. The importance and/or usefulness of this feature must have been considered minimal. I cannot recall whom stated this fact, but the pouch was never an "inventoried" item having a NSN assigned to it, so once supplies ran out, that was it. The addition of the pouch also terminated with the Phrobis contract as well.