So over the last year I've pieced together the core of what I hope to build as a 300blk pistol once the ATF brace rule is slain. So in the world of 8"-10.5" barrel makers, who are the stand outs for barrel accuracy under say $300? By accuracy I mean 1.5" 100yrd groups. The odinworks barrels seam to do ok and come with a AGB. Secondly I do intend to run suppressed with a adjustable gas block. But I also know there is some voodoo to picking the correct buffer weight to help match the barrel/gas setting. Is there any good write ups on this?

Current parts list is Aero M4E1 receiver set, Aero lower parts kit, AO precision government over run BCG, cmc drop in trigger, and a radian raptor charging handle.

Stay away from Odin Works. High price, low quality control.

Honestly the limit for accuracy with the 300 Blk won't be your barrel (most likely) it'll be the ammo. With that in mind, I just replaced the first 300 Blk barrel I ever owned (from back when the 300 was first introduced) and got a Ballistic Advantage barrel from MasDefense; it shoots great and should fit what you're looking for.

I use all my 300 Blk setups with a carbine buffer. If you need to go heavier, KAK Industries sells a buffer kit with individual weights you can change out. (You just drive the roll pin out of any standard carbine buffer and replace some of the steel weights with tungsten.)

+1 on Ballistic Advantage. They've always worked well for me

They also have an 8" barrel on sale:
https://www.ballisticadvantage.com/8-300-blackout-pistol-length-ar-15-barrel-modern-series.html

My setup:
KAK 8.5" barrel
https://www.kakindustry.com/contract-300-8-5-inch-pistol-melonite-barrel

Seekins Precision adjustable gas block:
https://seekinsprecision.com/parts-accessories/rifle-parts/low-profile-adjustable-gas-block.html

Armaspec Stealth recoil spring:
https://www.joeboboutfitters.com/Armaspec-AR-15-Stealth-Recoil-Spring-p/arma-153.htm

The buffer is the equivalent of a regular carbine buffer. It was super cheap compared to the JP silent capture spring but works well and has held up fine. It's not adjustable like the JP but you can buy two or three of the Armaspecs for the same price as the JP

I have the adjustable gas block dialed in to where it will cycle reliably but not be overgassed. I only shoot 200gn S&B out of it, always supressed with a Griffin Recce7. If you're going to be switching bullet weights frequently I'd recommend a gas block that's easier to adjust then what I've got. Mine needs an allen wrench to adjust, and to lock it in completely I have to take the handguard off. My handguard goes over the can so that complicates things

300 BLK in general is not an accurate caliber. 1.5" @ 100 is doable though with the right ammo.

+2 on Ballistic Advantage, though I am biased. Price per barrel, I don't think there is any manufacturer out there that makes one better for less.

There is no voodoo for buffer weight any different than a 5.56. If you're going to run subsonic, suppressed, you may have to play around with different weight buffers to get it to run reliably but standard AR15 buffer weights will work just fine.

For barrels, I think the ideal length is 9" but anything 8-10" is usually fine. Barrel length would more be dependent on what you want to use it for: home defense, hunting, plinking, etc.

Adjustable gas block, the Superlative Arms ones have been the best that I have used. They don't usually carbon lock like the cheaper ones will do after several hundred rounds.

We're talking 300 Blackout here of course, not 5.56 - in my experience, an adjustable gas block is not necessary. On those Ballistic Advantage barrels, in my experience an adjustable gas block does nothing of any benefit unless you're changing it to shoot supers suppressed, but even then you don't need it.

The 300 Blackout in the AR15 was intended from the beginning to be able to use 200+gr subsonics suppressed, and full power 110-125gr supersonics without adjusting the gas system. It's not difficult to set them up this way, and the Ballistic Advantage barrels I've used (own two, a 9" and a 16", and have assembled several others) seem good to go for this out of the box with a standard low-profile (non-adjustable) gas block and carbine buffer.

I DO use adjustable gas blocks on almost everything else, but on this application, I wouldn't bother.

The guys trying to use heavier bullets in full power supersonic loads will benefit more from an adjustable gas block, but the 300 generally doesn't perform well with those and that's outside its design envelope. Cheap 147gr bullets are common for blasting ammo, and that's fine, but the 150+ weight range is generally a poor choice for any sort of hunting or self defense in this round because velocity is too low for good expansion.

Sorry guys I was having to much fun with the m1 and forgot about this post.

You guys have talked me into the BA barrel. I'm leaning towards the stainless10.3" Hanson barrel paired with the atlas s 9" handguard. After looking at various buffers I'm also leaning toward the kak adjustable buffer to have the flexibility especially with the parts ban looming. I'd like to pair the kak with a JP polished spring but I'm unsure of who makes a tube with a truly smooth inside finish. Any recommendations for a mill spec carbine buffer tube that's actually smooth inside? Lastly what muzzle device would you run with?

Go look on BKings Firearms site, they've got a bunch of BA barrels on sale. I just got one.

BKings kicks ass, used them alot.

Yep, good stuff. And their "Mod0" uppers are a thermo-fit to most barrel extensions, which is excellent for an accuracy build.

In the past MasDefense always had the best deals on Ballistic Advantage barrels but this BKings sale has many of them beat.

You cannot go wrong with the Ballistic Advantage barrel for the Aero receiver. Ballistic advantage supplies barrels to Aero precision for their assembled uppers so you know they were made for each other. All you are basically doing is cutting out the labor cost to have Aero put it together for you.

And bed that bitch with some loctite!

That's on the list, along with looking into truing the receiver.

Stupid question time.... if I run the 10.3" barrel and an atlas 10.3" hanguard would that put the muzzel flush with the end of the handguard or inside of it?

Inside of it. The barrel length starts back inside the receiver - just in front of the ejection port opening. In most cases you'll need the handguard to be a shorter listed length than the barrel.

Exactly, unless you're planning on using a long flash can as a muzzle device.

I am, mainly the psa blast deflector. https://palmettostatearmory.com/psa-custom-series-30-caliber-fluted-flash-can-5-8x24.html