9mm AR Pistol Build – The Saga

AR’s are great because, as we all know, they are like adult Lego’s! You can change the caliber and performance of your pistol or rifle with the simple change of an upper. Some changes are easy and don’t require a lot of effort. Other builds are more difficult because there are a lot more complexities that require you to problem solve different variables. This is the story of how I built my 9mm AR Pistol and has a number of great lessons on what to do and what NOT to do when building yours. Check it out:

Parts List:


Provided by Brownells, this beefy bolt is what you need in a blowback 9mm carbine system. The added weight keeps the bolt steady while the bullet exits the barrel before the pressure drops to safe levels, allowing the bolt to cycle properly. Solid construction, great finish, very reliable.





Provided by Brownells, the conversion block is bottom insert and locks into place with your standard magazine catch. In order to make sure that the conversion block stays in place, the instructions recommend that you drill holes into your AR lower receiver and lock it in with pins. However, I found that cutting down nylon spacers to friction fit the conversion block within the magwell worked great. For the price, this is a great option for building a 9mm carbine.





Provided by Bronells, these magazines are built specifically to work not only with these conversion kits, but also dedicated colt pattern lower receivers. The mag is very good quality and cycles ammunition very well. The only issue you may run into is that the standard AR magazine catch may not be able to completely engage with the mag catch hole in the magazine. This can cause magazines to spontaneously eject from the magwell when firing.



FAXON – 8.5″ Taper, 9mm Pistol Caliber Carbine, Blowback, 4150 QPQ

Provided by Faxon, the barrel is the most important part of the build and Faxon continues to make outstanding products. The great things about this barrel, in particular, are that it is lightweight, the finish is great, and even after a long string of fire, it doesn’t seem to heat up at all. It’s threaded in 1/2 x 28, so most standard AR pattern flash hiders and brakes will fit, but you HAVE to make sure that they are bored out to 9mm or you will have a REALLY bad day.




Purchased by myself, this was, quite literally, the most important part of my 9mm build. The one problem that persisted throughout the entire process was that my magazines were ejecting from the receiver whenever the firearm was being shot. The reason for that is that the standard AR-15 magazine catch has a thinner shelf that the STANAG magazine mag catch hole rests on. Because the conversion block insert takes up more space, it takes away real estate from that top shelf that holds onto the 9mm colt magazines. The Spikes Tactical magazine catch has just enough extra material to securely hold your magazines in place and ensure reliable functioning of the build

Special Thanks to Geno at: https://blackrhinoconcealment.com/
Be sure to check out Guyinagarage’s channel for what happens next: https://www.youtube.com/channel/UCrZCwEZ3MBBd-TUu4auQvxg