OpenTube

.300 Blackout AR Pistol Build

Brownells, Inc.

213,137 views

In this build video, Caleb from Brownells walks through the complete process of building a 300 Blackout AR-15 pistol using top-tier parts from Aero Precision, Sons of Liberty Gun Works, Forward Controls Design, and more. From lower receiver assembly to upper setup, gas system pinning, and final accessories like optics and lights, this step-by-step guide is ideal for anyone looking to build or learn about a 300 BLK AR-15. The finished rifle will even be on display in the Brownells retail store.

Watch for helpful tips on staking castle nuts, installing precision triggers, setting torque specs, and more.

Chapters & Timestamps:

00:00 - Intro and Overview
00:47 - Parts Selection and Setup
3:45 - Lower Receiver Assembly Begins
14:10 - Castle Nut Installation and Staking
19:26 - Mag Catch and Bolt Catch Install
25:12 - Fire Control Group & Selector Install
33:06 - Grip and Brace Assembly
36:39 - Buffer Tube and Spring Install
37:06 - Upper Receiver Prep
40:08 - Dust Cover and Forward Assist Install
43:00 - Barrel and Handguard Install
46:12 - Torque Specs and Gas Block Pinning
54:00 - Muzzle Device & Shim Setup
58:23 - BCG, Charging Handle & Function Test
62:29 - Accessory Mounting
73:08 - Backup Sights & Red Dot Install
77:00 - Magazine & Range-Ready Wrap-Up
78:25 - Outro & Range Report Tease

20 Comments

@OLyonnais28 4 months ago

As a person with ADHD, I totally understand and appreciate the random thoughts and jokes.

@brianribble4236 3 months ago

Mr. Roger's of the gun world 😂

@carlh4350 10 months ago

Every time i do a build, I'm always amazed by the packaging trash. Everything is stacked and tidy sitting there waiting. Then an hour later you have a built gun and a bunch of packaging trash. Oh, usually a bunch of stickers too.

@jakepries779 9 months ago

love seeing another Iowa military guy putting this stuff together - Caleb is awesome!

@Majorpain32677 5 months ago

I'm building at PSA version of what you literally just built I'm a military veteran from South Carolina I get my guns from palmetto State armory but also get stuff from Brownells Great American company this video was perfect timing because this would be the first time I build a 300 blackout so thank you so much for this video and you have my subscription God bless

@Majorpain32677 5 months ago

Every time I do some type of gun build it seems like it's the easiest thing that gives me the problem I'm always at war with springs lol

@psycowilley3498 4 weeks ago

Great video. An extra roll pin is a great reason to do another build! Legos for men. I like the unfiltered, unedited honesty of the video.

@ryuffhhfvnmm 5 months ago (edited)

It's a beautiful day in the neighborhood Mr Roger vibe

@chrisg3162 10 months ago

Speaking of user-requested videos: You did a choke-tube video a few years back and teased a video on patterning a shotgun. This is my follow up vote to see that, and with Thanksgiving coming up, it's timely :D

@Nordic67 4 months ago

Caleb is such a great guy, his personality and everything he does. I watch all his videos. Brownells is getting my business for that magnetic screwdriver set. Always enjoy seeing everything and all the advice. Thanks for the videos Brownells. I wonder what Caleb will use if Aero precision becomes unavailable. Super bummed we cant get Aero stuff. I really hope they stay going or someone else buys the company. Aero lowers are my favorite.

@paulhoughton4813 10 months ago (edited)

I hands-down like watching you and your builds more than anybody else out there. You’ve got a great voice for it. You explain things well, thank you so much! My daughter did my last build for me in her shop. She’s self-employed and has a helicopter shop because she’s a helicopter mechanic and rebuild helicopter motors. I had her watch you before she did it.

@JSmith-ou3sk 10 months ago

Now I wanna build. Good explanation. Time for the parts list.

@VexxumSDMF 7 months ago

I figured you would do a headspace inspection.

@ramjabar6459 4 months ago (edited)

All these fancy fixtures...I just assemble it all in my lap! I find it very soothing watching you put it all together.

@ChaseDog177 10 months ago

I love the build series so much. Especially when he has guests on (having his commanding officer on has been the best one) but best part of this video was when Caleb got so excited finding the surefire sticker lol

@mrmongo656 10 months ago

This reminds me that I have a full AR system waiting for me to build it up in 300 blackout. Thanks for a very informative video, Caleb, because I needed to pick up a few things I’ve been leaving out in the past.

@CFurnace-72 4 weeks ago

I like to slightly grind the flats on the upper before installing the barrel to ensure good metal metal stress free mating barrel to the upper receiver.

@wessmith-q3p 2 weeks ago

thank you. my lower upper lower aero 300blk built my self.. 10 years ago.. your great. hit 330 yard moa2 220 grain sub his 250 2 moa 150 supers. love it. like the john wanye. it does. guess need to build a new one..