Sounds to me like he is referring to an M548 Ammo carrier. Here is one:
and a website with data on it: http://www.fas.org/man/dod-101/sys/land/m548.htm
AFV Club used to have a model of it, I think it is out of production though, this is what it looked like:
It is an excellent kit and is frequently available on Ebay.
Good luck.
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