Uh, guys, I hate to break it to you but the HK USP does NOT come with a lock on the mainspring housing, or anywhere else for that matter (I own four, so I oughtta know). You may be confusing this weapon with an inferior model like the 1911. Also, Half-Price, the USP Full-Size .40 magazines come ONLY with the flat baseplates. By contrast, the Full-Size .45's (and compact USP's) come standard with the extended baseplates.