From the current Federal Firearms Regulations Reference Guide:
"(31) The term "large capacity ammunition feeding device" -
(A) means a magazine, belt, drum, feed strip, or similar device manufactured after the date of enactment of the Violent Crime Control and Law Enforcement Act of 1994 that has a capacity of, or that can be readily restored or converted to accept, more than 10 rounds of ammunition; but
(B) does not include an attached tubular device designed to accept, and capable of operating only with, .22 caliber rimfire ammunition."
Caution, your local regulations could and may be stricter.
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Mike