With a "bullet button".
DOJ regulations30515(b) For purposes of this section, “fixed magazine” means an ammunition feeding device contained in, or permanently attached to, a firearm in such a manner that the device cannot be removed without disassembly of the firearm action.
5469 (a) "detachable magazine" means any ammunition feeding device that can be removed readily from the firearm with neither disassembly of the firearm action nor use of a tool being required. A bullet or ammunition cartridge is considered a tool. Ammunition feeding device includes any belted or linked ammunition, but does not include clips, en bloc clips, or stripper clips that load cartridges into the magazine.