The STUD magazine that fits the FX Panthera, Dynamic is not just a standard Maverick/Dreamline etc. magazine with a taller lid fitted onto the top of it like the FX Magazines. This magazine was specifically designed to stage, index and feed heavy slugs (and pellets) into the Panthera/ Dynamic in a truly superb fashion. Its center rotor is about 2mm taller than the competition and reaches up very close to the inside of the lid. This allows excellent contact and indexing of slugs up to 13mm in length. This magazine, like our Impact and Maverick mags, has a center rotor that rides on very precise roller bearing allowing friction free rotation. When the magazine indexes, you will feel the immediate staging of the round into the STUD Pocket. The STUD pocket is in the position commonly known as the staking position. What makes the STUD Pocket unique is it causes the round to be shot next, to be held in a highly accurate position which precisely aligns with the center of the magazine, and of course the Panthera barrel. Just look at any other non-STUD magazine with the round in the staking position, and then compare it with the STUD magazine. You will see and feel the difference as you advance the slug into the barrel.