A loader (10) facilitates loading loose rounds into a firearm magazine (60). It comprises a body (12) that fits on and is locked to the magazine using a locker (40). A spring-loaded press (30) with a plunger (34) is coupled to the body and is tiltable from above to between the magazine's lips (64). To load a round, the user fits the loader onto and locks it to the magazine and forces the spring-loaded press down so the plunger pushes the topmost round and/or follower down enough to insert a new round, case first, until it meets the plunger. Then the user reduces force on the press to allow the plunger to be lifted up so that the plunger is cleared from the magazine, whereupon the user can nudge the partially inserted round rearwardly to its final position in the magazine.