Home AR-15 .300 Blackout AR Pistol Build

.300 Blackout AR Pistol Build

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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

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26 COMMENTS

  2. 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.

  3. Speaking of user requested… This is my first video from the channel, I definitely will be coming back! but a video I would like to see is an AR build with the cheapest quality parts possible modified to be extremely high quality, so you could take a really budget build and get incredibly high quality out of it for a really cheap price, if you're willing to modify the parts or do any kind of tweaks to it or whatever is required to get that part where it should be. For instance, if you have the scales or whatever to balance or the micrometers to ensure tolerances are perfect, things like that.

    Maybe do three tiers of runs through that style of playlist so then that way you could have bargain basement parts turn to mid-grade, mid-tier parts that you're taking up to high-end. and high-end parts and setups that take you to God tier.

    I feel like it would teach so much in why you purchase what you purchase, what is a balance build, and by balance I mean you don't put like a $1,000 bolt carrier on a budget AR. That's just silly. So things like that. Also, it would teach you what tools you need to take things to the next level because that's also a big part of it as well.

    If something like that already exists on the channel, I would definitely like to be pointed at it, but I'm gonna look through a couple of videos and see what you guys got. I think you got some really good stuff here so far.

  5. 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 😀

  8. Your improper castle nut installation, improper barrel installation, improper muzzle device installation, and lack of proper thread locker use on screws is comical!!! Maybe you should take the class from School of the American Rifle to actually learn how to build AR's properly!!!

  13. I built my first AR 15 lower with a match trigger , it is so much fun , and I learned alot about that rifle . I have test shot it with a upper from my other store bought rifle , it runs great.
    I have my upper ordered, stainless 16", with an A2 stock . I'm excited.
    I want to build another one. Maybe a pistol one day.

  16. Yo, what's that noise in the background. it's like cross between a dinging or beeping, high pitched. oh wait. nevermind. its a music bed that's not turned up high enough. Personally, and i'm not yelling, I don't care for music beds playing the whole time that a person is doing something in a video. Especially if it basically is 15 or 30 seconds of a repeating loop. but I digress. Thanks for posting this. I had a few L9 SOLGW lowers at my gunsmith that were waiiting for me to send him the parts kits and whatnot, and I finally did. I used Sons' stuff on both, but I did get the Sons L2 trigger on one of them. I've not put an uppper on either yet, but maybe will at some point in the coming year.

  17. Good timing, I just bought my first 300blk AR "pistol" and took it to the range yesterday, had a blast, especially unsuppressed with supers. Its a DPMS Kitty Kat, 7.5 inch, it ran great with subs and a can (Wolfman) though it was a bit loud for my taste but it also ran great unsuppressed with supers. Its actually gassed pretty light too, I was frankly surprised how reliable it was given its a PSA and I've heard some things so I wasn't sure what to expect but I'd definitely recommend it. It works and its fun as hell.

  23. So I’m currently building an ar10. I didn’t see you headspace the bolt to the BCG in this video and it’s something im worried about in my build. I hear a lot that you don’t need to headspace ar15s because of mil spec tolerances. But what about ar10s (DPMS style)? I’m mostly just worried if I have to drop $80 on a go and no go guage for something I’ll use once and never again

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