JP upgraded their awesome GMR-13 9mm AR rifles with a new lower receiver that features last round lock back, an improved magazine release and a flared magwell. The new model designation is GMR-15. Fortunately JP has made the new 9mm lower available in kit form. The “JP GMR-15 9mm Billet Lower Receiver Kit JPGMR15LRK1” would be my choice for a 9mm AR build today.

From JP Rifles: For the home builder with a 9mm Pistol Caliber Carbine project, this GMR-15™ billet lower receiver accepts Glock G17 magazines and will mate to any Mil-spec compatible upper receiver. This kit includes all proprietary bolt catch, magazine catch and ejector components required for function. Read more about the GMR-15 platform here. Visit JP