Nerf Alpha Trooper 18-Dart Drum Magazine Problem.?

Whenever I load the 18 dart drum magazine into my Nerf Alpha Trooper, it only brings trouble. Randomly during the time I'm firing my Alpha Trooper with the drum magazine, the bullet that comes before the bullet I just fired doesn't move up, so I fire nothing. This isn't a trouble with my Alpha Trooper, as it works fine with other clips and the same problem happens in my other Nerf guns when I use the drum magazine. Is there a way I can fix my Alpha Trooper's 18 dart drum magazine? If I have to open it up then that is fine. Thanks for your help!