A collapsible buttstock which is adapted primarily for use with military and tactical carbines, is supported by an extension tube which is connectable to the receiver of a carbine on which the collapsible buttstock is to be mounted. A storage enclosure is formed in the body of the buttstock and is sized and dimensioned so that it can receive a clip or magazine, typically able to carry 20 rounds, that is usable with the carbine on which the collapsible buttstock is mounted. The enclosure is provided with an openable cover that is hingably attached to the buttstock body. An easily operable cover latch assembly is usable to secure the cover in a closed position while facilitating expeditious opening of the cover to afford access to the spare magazine storage enclosure.