Need help with AR-15 300blk build…my first build

Moderators:gds, bakerjw, renegade

Post Reply
Gunther300
New Member
Posts:6
Joined:Tue Mar 22, 2022 7:56 am
Need help with AR-15 300blk build…my first build

Post by Gunther300 » Tue Mar 22, 2022 8:21 am

So I’m building a 300 blackout AR 15 with a Faxon Gunner 16inch barrel, Faxon Light weight BCG, carbine buffer tube. I was going to run a Carbine gas system with adjustable gas block if possible. I’m also not sure of what kind of buffer an buffer spring to use. I’d like to run supersonic if that helps with anything. If anyone could help or point me in the right direction I greatly appreciate it.

BulletFlight for Android
ReadyAimDuck
Silent But Deadly
Posts:161
Joined:Tue Jul 14, 2020 11:08 am

Re: Need help with AR-15 300blk build…my first build

Post by ReadyAimDuck » Tue Mar 22, 2022 6:08 pm

A standard weight BCG with a standard buffer spring and somewhere between a carbine buffer and H2 depending on your gas port diameter, is going to be what I would recommend. If you already have the lightweight BCG, and you're going to want to use that, then you'll end up using a heavier buffer than you would with a standard weight BCG. I'd recommend keeping a few different weight buffers on hand and see what runs best.

Gunther300
New Member
Posts:6
Joined:Tue Mar 22, 2022 7:56 am

Re: Need help with AR-15 300blk build…my first build

Post by Gunther300 » Wed Mar 23, 2022 2:23 pm

Yea I already have the light weight BCG. So should I buy a couple like an H3 H2 buffers? Is there a certain spring I should use. I feel like I’m making this difficult but I really don’t know so that why all the questions. I just don’t want to damage anything ya know.

User avatar
dellet
Silent But Deadly
Posts:6824
Joined:Fri Nov 30, 2012 1:25 pm

Re: Need help with AR-15 300blk build…my first build

Post by dellet » Wed Mar 23, 2022 2:40 pm

You want to shoot supersonic, or will only shoot supersonic?

It makes a huge difference. Even if the rifle is set up as intended, it will be over gassed for supers. That’s the only way to allow it to cycle subs.

Total mass weight is what matters, based on gas pressure. So if you keep a standard port, and reduce the weight of the carrier, you either need to add weight to the buffer, or increase spring tension. Or lighten the load.

There are so many combinations once you start to step outside of how the system was designed, you need to define what you are trying to accomplish. Then you have a direction that you can follow. Other wise it’s just a pointless circle of compensating for the last modified part installed.
300 Blackout, not just for sub-sonics.

Gunther300
New Member
Posts:6
Joined:Tue Mar 22, 2022 7:56 am

Re: Need help with AR-15 300blk build…my first build

Post by Gunther300 » Wed Mar 23, 2022 4:13 pm

I would like to run just supersonic. The barrel is a carbine length gas port. What type of combo would I need to be able to shoot the supers? Would I go with an adjustable gas block and a heavier buffer like an H3. This is where I get confused with the super&sub round. I wasn’t sure if you could have it shoot both or just lean towards one side. But yes I would like to just run supers and if I could run subs that be cool but if not then I’d want to run supers.

Gunther300
New Member
Posts:6
Joined:Tue Mar 22, 2022 7:56 am

Re: Need help with AR-15 300blk build…my first build

Post by Gunther300 » Wed Mar 23, 2022 4:34 pm

This is what I have so far for the build.
Anderson stripped upper
Anderson stripped lower
Faxon LW BCG
Faxon 16in 300 Gunner Profile 1:8 twist, carbine-length
V-Seven Ultra-light door rod
V-Seven Titanium take down pins
V-Seven Titanium mag catch release
V-Seven Light-weight buffer tube (carbine)
V-Seven Titanium buffer retainer
Magpul MOE-K2 Grip…

So far that’s all I have purchased for the build as of now. Looking at the V-Seven extreme temp. Gas tube at carbine length but not sure about AGB & Buffer&Spring.

Any help be great… Looking to run SS.

ReadyAimDuck
Silent But Deadly
Posts:161
Joined:Tue Jul 14, 2020 11:08 am

Re: Need help with AR-15 300blk build…my first build

Post by ReadyAimDuck » Wed Mar 23, 2022 6:44 pm

You don't need an adjustable gas block. They're nice if you want to tune a gun to run a certain way for you by limiting the amount of gas in the system and/or bleeding it off. Typically, this is done to achieve the lowest amount of felt recoil while maintaining functionality, slight sound reduction while suppressed (claimed by bleed off gas blocks), etc. But, remember, an adjustable gas block can't increase the amount of gas flow for you, it can only limit it. If your application calls for that kind of tuning then you may want an adjustable gas block. Otherwise, you'll be fine running supersonic loads with a standard gas block. For me, I like adjustable gas blocks on uppers I use subs and supressors with, and for range fun. I like standard blocks on rifles I want to have max reliability, although some would argue that a good adjustable block is very reliable if installed and used properly.

Like dellet said, there are so many combinations that can produce the same results for you. And some of it is going to depend on your gas port diameter. If it were me with the parts listed and the lightweight BCG, I would start with a standard spring and an H2 buffer and see what the results are. Chances are if you are building a rifle, you are also the type of person that is going to like to modify/experiment/fine tune. So, I would recommend trying a couple of different buffer weights to see how the recoil feels to you, see how the brass is ejecting and the bolt locking back reliably, etc.

Gunther300
New Member
Posts:6
Joined:Tue Mar 22, 2022 7:56 am

Re: Need help with AR-15 300blk build…my first build

Post by Gunther300 » Sat Mar 26, 2022 3:25 pm

Can I still use an adjustable gas block or should I try a regular one first. If it’s possible for me to run a AGB I’d like to. You’re absolutely right I’m someone who going to want to fine tune it and get the softest recoil possible with it still being reliable

ReadyAimDuck
Silent But Deadly
Posts:161
Joined:Tue Jul 14, 2020 11:08 am

Re: Need help with AR-15 300blk build…my first build

Post by ReadyAimDuck » Tue Mar 29, 2022 7:22 pm

Yes, you can use an adjustable gas block. On the most wide open setting it should allow the same amount of gas as a standard block. So you’ll have the option of allowing less gas into the system, if you choose, from there.

Post Reply