The Pocket
Dropping a spare magazine into a pocket is certainly convenient. It also gives the magazine complete freedom to move around.
Without a pocket carrier, it can rotate, turn upside down and get tangled up with coins, keys, breath-mint wrappers and who knows what else. None of this is beneficial when you need a clean, predictable draw.
A dedicated pocket magazine carrier works much like a pocket holster. It keeps the magazine in a consistent orientation and uses shape, texture or a hook to remain in the pocket while the magazine comes out. That last part matters. Drawing the magazine and its carrier as one unit creates an embarassing and potentially harmful situation.
Pocket space is also a limited natural resource. If you keep your spare magazine there, make it a single-occupancy residence.
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