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A company called CROSS Industries makes 10 round AR-15 magazines with a specially designed floorplate that allows to couple the magazines by attaching the floorplates together.

The result is an assembly consisting of two 10 round magazines attached together upside down with overall dimensions similar to a standard 30-round magazine



The company doesn’t clearly specify on their website at what applications this coupling solution can be most beneficial. I think that most likely, the main market for this product will be the states and countries that have a 10 round magazine capacity restriction.

By having such coupled 10 round magazines, you should still comply with the legislation but have an arguably quicker reloading possibility and overall magazine shape similar to the 30-rounder fitting the standard pouches. Now, keep in mind that these are just my assumptions and you need to make sure you are not breaking your local laws.
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