.300 Questions

[Danny46]

Finally around to getting a .300 done up and have a few questions.

1) Barrel length, I know someone posted some kind of data regarding barrel length/performance (CJ?) but cant find it. From what I understand you arent losing a whole lot of performance with a <16'' barrel and the shorter length lends itself better to a suppressor, correct? Is there a sweet spot barrel length for this?

2) Is there anything different I need to do with an upper going the "pistol" route vice and actual rifle? My intentions are just to get it done asap so I can hunt with it this season, then getting the SBR stamp done later on when I have the time/money. Wasn't sure if there was something I needed to do with the gas system differently with this route.

3) Brands: Any I need to stay away from? I started this out as a budget build but dont want to get something thats going to break/blow up/fail after mild use.

4) What twist rate should I be looking at for this?

Been keeping an eye out for cyber monday sales on this stuff but havent pulled the trigger yet. I have a stripped upper receiver and basically need everything else.

[LANTIRN]

Sounds like you are doing the same kind build I am right now. The 300blk was designed around a 8 or 9" barrel and you gain almost nothing going to 16" from my understanding. I will be building a pistol with a KAK buffer tube and Sig sbx brace (possibly doing an sbr later but unsure right now). Red X has this upper I will be buying, plus I will put some backup irons on it and a primary arms micro dot most likely.

Upper

http://shop.redxarms.com/9-RXA15-300-BLACKOUT-EVO-KEYMOD-UPPER-1-7-TWIST-9300AACEVOMOD.htm

Edit, I have a red x on my wife's AR and I have been happy and their prices are hard to beat. I believe several members have built guns using them. As for the gas system, leave it at the pistol length. This round was designed to fire suppressed and unsupressed reliably with a non adjustable gas system so just don't mess with it. I believe all uppers are built with a pistol length system.

[Danny46]

Dang thats not a bad price at all. I wanted to build my own but wouldnt be adverse to getting one like this. I'll be hunting with this rifle so will be getting a magnifying optic but had also planned on the sig brace.

[motoman]

Like LANTIRN said, the 300Blk was designed to run in the SBR platform but also performs very well when subsonic ammo is used with a suppressor. I would look for a 1:7 or 1:8 twist barrel if you're planning to run subsonic ammo or a suppressor in the future on a barrel 10 inches or shorter. CJ can speak to the issues he ran into with a piston setup and would probably recommend going DI. You can run a carbine length gas system and be fine. I think some companies even make a "pistol" length system for SBR use, which is slightly shorter than carbine length. As far as brands, that's subjective. I've got a CORE15 upper and a CMMG barrel and haven't had issues with either on my .300BLK SBR.

[lilvega]

I used the CMMG barrel too. 8.5" long and 1 in 7 twist.
The barrel was pricey compared to some others but it is quality. I built my upper with decent stuff and have about $600 in it. It is super quiet with my AAC SDN6 and 220gr loads.

[Danny46]

I used the CMMG barrel too. 8.5" long and 1 in 7 twist.
The barrel was pricey compared to some others but it is quality. I built my upper with decent stuff and have about $600 in it. It is super quiet with my AAC SDN6 and 220gr loads.

Almost pulled the trigger on the completed upper but I started out wanting to build it myself. Got a CMMG barrel yesterday and a few other misc cyber monday deals. Almost have everything!

[LANTIRN]

Almost pulled the trigger on the completed upper but I started out wanting to build it myself. Got a CMMG barrel yesterday and a few other misc cyber monday deals. Almost have everything!

What barrel length did you go with?

[Danny46]

8" 1 in 7 twist. Need to get a lowpro gas block and a couple other nicknacks and I'll be ready to throw it all together.

[matts5.0]

Is 300 blk any better than 7.62x39 in a full length barrel?

[LANTIRN]

Is 300 blk any better than 7.62x39 in a full length barrel?

They are supposed to be comparable, but I believe .300 performs a little closer to .30-.30. The main advantage to .300 is it was designed for a short barrel and to be shot suppressed with a non adjustable gas system. That plus it uses all the same parts for an AR15 except the barrel and it makes it worth considering over an AK, in my opinion, especially for the guys who already own an SBR'd AR lower.

[Danny46]

They are supposed to be comparable, but I believe .300 performs a little closer to .30-.30. The main advantage to .300 is it was designed for a short barrel and to be shot suppressed with a non adjustable gas system. That plus it uses all the same parts for an AR15 except the barrel and it makes it worth considering over an AK, in my opinion, especially for the guys who already own an SBR'd AR lower.

I guess I never thought this through completely but I always thought when you register an SBR that the upper was the registered part? are you saying that you register the lower as an SBR? Does that mean I could theoretically have more than one short barreled upper receiver and just swap them onto the lower as I see fit?

[LANTIRN]

I guess I never thought this through completely but I always thought when you register an SBR that the upper was the registered part? are you saying that you register the lower as an SBR? Does that mean I could theoretically have more than one short barreled upper receiver and just swap them onto the lower as I see fit?

Correct.

[IHaveAMustang]

I guess I never thought this through completely but I always thought when you register an SBR that the upper was the registered part? are you saying that you register the lower as an SBR? Does that mean I could theoretically have more than one short barreled upper receiver and just swap them onto the lower as I see fit?

Best part of having an AR-15 SBR. I have 9mm, 5.45x39, 5.56, and soon .300BLK

[Danny46]

Best part of having an AR-15 SBR. I have 9mm, 5.45x39, 5.56, and soon .300BLK

Wow, that is awesome.

What are the best options if I just want the buffer tube without the Sig brace and all that? I dont mind the sig brace but dont care to pay for it since its almost as much as the tax stamp, but I would like to have this rifle up and running asap.

Also how is the reliability with hypersonic rounds? (no suppressor)

[IHaveAMustang]

Wow, that is awesome.

What are the best options if I just want the buffer tube without the Sig brace and all that? I dont mind the sig brace but dont care to pay for it since its almost as much as the tax stamp, but I would like to have this rifle up and running asap.

Also how is the reliability with hypersonic rounds? (no suppressor)

I have a Pistol that I put a Red X Arms 10" upper on and I just wrapped my buffer tube with para cord and sealed it with a cane cap. It looks decent enough.