For the most part, there isnt a lot that makes one gun stand out from the others on the surface. AR-15 9MM BOLT CARRIER GROUP FOR GLOCK AND COLT FAXON FIREARMS (In Stock) $160.99 - $189.99 4.9 (6) 9MM CARBINE BOLT CARRIER GROUP SHORT STROKE COMPATIBLE J P ENTERPRISES (In Stock) $246.99 0.0 MKG GUARD BARREL & BCG KIT 16" 9MM CMMG (In Stock) $496.99 0.0 AR-15 BARREL & BOLT CARRIER GROUP SETS 9MM CMMG (In Stock) $439.99 - $465.49 5.0 (1) You're going to end up spending way more time and money and frustration than it's worth. There are a few items that will not be compatible, however, such as a BAD lever, which wont work because of receiver geometry. AR-9 9mm BCG + 1/2x28 Barrel - Choose Size $109.95 - $124.95 IN STOCK View More Grid Defense 1/2x36 Dimpled Linear Compensator Flash Can MSRP: $39.00 SALE PRICE: $22.86 IN STOCK Add to Cart AR-9 9mm BCG + 1/2x36 Barrel + Magwell Adapter - Choose Size $174.95 - $199.95 IN STOCK View More 9mm being one of the most popular rounds on planet earth, complete AR9 uppers are chambered in Herr Luger's cartridge and engineered to integrate with the AR platform. Another version I am personally excited about is a 9mm variant. Evolution Weapon Systems had begun working on a prototype bufferless bolt carrier group system for the AR-15 platform, and Instagrammer thegatman had posted a few teaser videos. A PCC upper must shoot 9mm ammunition as everything from the ejection port size to the BCG changes to support that specific cartridge. //