It's become necessary to add a caveat when using the the term "Assault Rifle" (eg "'assault rifle' as defined by x,y, or z").
Padre, Ebay is confusing, but they have an outright ban on any magazine holding more than 10 rounds. It's not necessarily because the mag is "assault rifle" related. Here is a link to Ebay's firearms and weapons rules:
http://pages.ebay.com/help/policies/...ns-knives.html
Prohibited: High-capacity magazines with a capacity to accept more than 10 rounds—or magazine extenders