Build a 300 Blackout AR Upper

[DadSmith]

I'm going to build a new 16" upper in 300blkout.
I talked to my buddy he said there are a lot of ways to build it, and it depends on what bullet weight I was wanting to shoot with it.

So 300blkout guru's I'm going to rely upon your wisdom for my new build.

My main bullet weight will be 125gr, and maybe 150gr. I'm thinking 1/8 twist would be good for that, but want to get proper opinions before investing in a barrel.

My buddy said his 300blkout runs better with pistol length gas system. He runs 220gr+ in his though. What length gas system would I need for lighter bullets?

I also plan on building it with an adjustable gas block as well. Any recommendations on one?

Anything else you can think of let me know.

 

[R3p1lc3]

I'm no expert but I do have experience with 300blk. 16" is overkill IHMO, Most loads you'll be done burning powder about 10"-12". Of course that can vary if your running your own loads and play with powder. Most of the stuff you'll buy off the shelf will be burnt withing that length.
Questing is.. what do you plan to use it for mainly?
If you do go with a longer barrel. go with carbine length gas system, not a pistol length.. you'll run into timing issues in my experience, changing round weight/load can play into that as well. An adjustable gas block will be your friend with 300blk as you do play with different projectiles and loads, I'd consider it a must.

edit: On gas blocks there are a plethora to choose from.. Just look for feedback when choosing you should be fine. the 40-60$ range in my experience work just fine.

 

[AndreusMaximus]

I did a 300 blackout upper build with a 16" barrel and pistol length gas system. It ran flawlessly with 220gr subs, but with 125gr supers it would cycle too fast and I would have failures to eject every few rounds.

I bought this gas block just because it was cheap and I don't really have a serious use for the rifle yet. I haven't run it very extensively, but it seems well made, and has worked fine for me so far:

Aero Precision Adjustable Low Profile Gas Block w/ Aero Logo Up to $7.01 Off w/ Free Shipping — 4 models

Shop Aero Precision Adjustable Low Profile Gas Block w/ Aero Logo | Up to $7.01 Off 4.7 Star Rating on 91 Reviews for Aero Precision Adjustable Low Profile Gas Block w/ Aero Logo...

www.opticsplanet.com

 

[edwea]

I second the aero agb. Centurion thermal fit upper and faxon barrel ftw.

Faxon Duty Series 16", Gunner, 300 BLK, Carbine-Length, 4150 QPQ Nitride AR-15 Barrel

Made from 4150 CMV, this AR-15 barrel is the pinnacle of value. Faxon's Gunner profile combines two of the best profiles ever, Gov't and Pencil.

faxonfirearms.com

 

[Kirk Freeman]

I did not build, I bought LWRCI M6 DI. Shoot the 110 Federals, which it loves, no issues. Try to find photo tonight.

 

[DadSmith]

I did not build, I bought LWRCI M6 DI. Shoot the 110 Federals, which it loves, no issues. Try to find photo tonight.

Do you know what the gas system is, and barrel twist rate is?

 

[R3p1lc3]

I like the 110gr vmax for my shorty 7.5" with 1/8
Almost all barrels I've seen are either 1/7 (good for longer barrel less rpm) or 1/8 - most common

 

[Kirk Freeman]

Do you know what the gas system is, and barrel twist rate is?

Yes, it is internal piston (DI) and 1/7".

IC DI Standard 300 BLK

www.lwrci.com

 

[Cavman]

Built a cheap hunting AR. Used a stoner 16" barrel with pistol length gas tube. Been using it for years. Shoots surprisingly 1 inch groups with barnes 110. Hell think the barrel was only like 80 bucks at the time

 

[DadSmith]

Built a cheap hunting AR. Used a stoner 16" barrel with pistol length gas tube. Been using it for years. Shoots surprisingly 1 inch groups with barnes 110. Hell think the barrel was only like 80 bucks at the time

Are you using a 1-7 twist also?

 

[DadSmith]

Yes, it is internal piston (DI) and 1/7".

IC DI Standard 300 BLK

www.lwrci.com

So going to be different regarding gas system. Mine will be just the normal DI.
I've got to figure out the best length though. Carbine, or pistol?
Will 1-7 be a little fast for 150gr?

 

[Cavman]

Are you using a 1-7 twist also?

Yes sir

 

[Kirk Freeman]

Here's my LWRCI, Kirkified with a Centurion AMT trigger, Canookian tri-rails, Pro III BUIS and a PA GLX 2X:

 

[Dog1]

This is a 16 in 300 Blackout that I built. Has a Wilson Combat 300 Blackout Barrel Midwest Industries rail it's just an Anderson lower with a mil-spec parts kit in it. It has the Hera arms buttstock and foregrip on it. It runs great with both 147 grain supers and 110 grain supers. Suppressed or unsuppressed. To be honest it sets in the back of the gun safe cause I don't mess with 300 blackout anymore. To be honest I was going to put it up in the classifieds. If you're interested shoot me a message

 

[DadSmith]

View attachment 335907

This is a 16 in 300 Blackout that I built. Has a Wilson Combat 300 Blackout Barrel Midwest Industries rail it's just an Anderson lower with a mil-spec parts kit in it. It has the Hera arms buttstock and foregrip on it. It runs great with both 147 grain supers and 110 grain supers. Suppressed or unsuppressed. To be honest it sets in the back of the gun safe cause I don't mess with 300 blackout anymore. To be honest I was going to put it up in the classifieds. If you're interested shoot me a message

I've got everything I need except for barrel, adjustable gas block, and tube. I'm just trying to figure out what I need to get barrel twist rate wise, and gas system length to run the lighter bullets.
Thank you for the offer though.

Do you happen to know the twist rate on that barrel?

 

[Dog1]

I've got everything I need except for barrel, adjustable gas block, and tube. I'm just trying to figure out what I need to get barrel twist rate wise, and gas system length to run the lighter bullets.
Thank you for the offer though.

Do you happen to know the twist rate on that barrel?

1/7 on the twist.

It's a very accurate barrel.

 

[DDadams]

SLR Rifleworks series of Sentry gas blocks are typically regarded as some of the best on the market.

I haven't been using adjustable blocks lately after starting to use BRT Eztune gas tubes but for a 300BO if you plan on going between supers and subs it would be basically necessary.

 

[DadSmith]

SLR Rifleworks series of Sentry gas blocks are typically regarded as some of the best on the market.

I haven't been using adjustable blocks lately after starting to use BRT Eztune gas tubes but for a 300BO if you plan on going between supers and subs it would be basically necessary.

So if I don't plan on using subsonic I probably don't need the adjustable gas block?
I want it mostly for deer hunting so supers is what I plan on going with. 125gr possibly 150gr.

 

[DDadams]

So if I don't plan on using subsonic I probably don't need the adjustable gas block?
I want it mostly for deer hunting so supers is what I plan on going with. 125gr possibly 150gr.

With just supers you shouldn't need an adjustable gas block. Not unless you want to fine tune it to be super soft or something. It'll run just fine fixed gas on supers unless you get a niche barrel that was made specifically for subs.

Edit:
And if you did want to tune the gas down after you could just change the tube to a BRT eztune gas tube instead of the whole block.

 

[DadSmith]

With just supers you shouldn't need an adjustable gas block. Not unless you want to fine tune it to be super soft or something. It'll run just fine fixed gas on supers unless you get a niche barrel that was made specifically for subs.

Edit:
And if you did want to tune the gas down after you could just change the tube to a BRT eztune gas tube instead of the whole block.

I never even thought about a BRT EZtune tube.
See this is why you get as many opinions as possible. More minds thinking on a topic leads to more options.