The AR-15 is one of the most customizable rifle platforms ever designed. Adjustable stocks, free-float handguards, trigger upgrades, optics systems — the aftermarket is virtually limitless. Yet for all its modularity, the original AR-15 design carried forward one significant ergonomic limitation straight from its military origins: it was engineered primarily for right-handed shooters. The standard AR-15's controls reflect this clearly. The magazine release button sits on the right side, ac …