Just completed my SBR build - 300 blk

[MJDGator]

You forgot to add "Suppressor" to the list.



For the trigger choices I would go ACT and use the 200 that I saved on a tax stamp. I already had an SD-E in my V5 and really liked that trigger so I figured it would be great in my DD MK18 and sure enough, I liked it in there as well. When I built my 11.5 SBR I decided to get the ALG ACT since I went over budget on my rail. The ACT is fantastic and I have no thoughts of switching it to an SD-E, or any two stage trigger in the future. I usually shoot my SBR's at close distances and the ACT fits the bill nicely. When I start building an 18 or 20 inch rifle I plan on taking the trigger from my MK18 and getting an ACT to put in its place.

The rifle looks good!

Thanks for the input. For guns intended purpose I think you are 100% right. The ALG ACT is the way to go. I am not planning on trying to get .5" groups at 100 yards. Forgot the suppressor lol. That will come at some point I think. A guy I used to work with was giving me a hard time about going with a 300blk SBR without a suppressor. Granted he is a suppressor nut. I think he has a suppressor for every gun he owns lol.

[MJDGator]

Here are some updated photos:

[MJDGator]

Ballistic Advantage tested my barrel and did not have any issues but sent me a new barrel anyways. I got it out to the range today and it ran like a top. Just needs the o-ring on the extractor spring. Since BCM's site states that they recommend the o-ring on their 300blk rifes I am considering this a non-issue (AAC also has an o-ring installed on their bolts). I do think something was a little funky on the first barrel. Not sure what but now without the o-ring I get failure to eject with the case laying loosely on top of the magazine instead of a being stuck in the chamber and no odd scratches/rings on the spent cases.

[Benito]

Ballistic Advantage tested my barrel and did not have any issues but sent me a new barrel anyways. I got it out to the range today and it ran like a top. Just needs the o-ring on the extractor spring. Since BCM's site states that they recommend the o-ring on their 300blk rifes I am considering this a non-issue (AAC also has an o-ring installed on their bolts). I do think something was a little funky on the first barrel. Not sure what but now without the o-ring I get failure to eject with the case laying loosely on top of the magazine instead of a being stuck in the chamber and no odd scratches/rings on the spent cases.

I've never read anything about BCM recommending the extractor spring O-ring on .300 BLK rifles. Why would this be any different than with a 5.56?
If anything, the higher chamber pressure and presumably faster bolt carrier speed would require less extractor tension. I could very well be mistaken.

[MJDGator]

I've never read anything about BCM recommending the extractor spring O-ring on .300 BLK rifles. Why would this be any different than with a 5.56?
If anything, the higher chamber pressure and presumably faster bolt carrier speed would require less extractor tension. I could very well be mistaken.

Copied directly from their website. If you go to their 300blk barrels listed on their site and click on a barrel to read the description. It is the last sentence right above the bullet points giving the barrel specs: "BCM also recommends running the Crane O-ring (provided with all BCM Bolt Carrier Groups) over the extractor with 300 Blackout."

I thought 300 blk had the same chamber pressure as .223 which is less than 5.56?

[Clint]

I've never read anything about BCM recommending the extractor spring O-ring on .300 BLK rifles.
Why would this be any different than with a 5.56?
If anything, the higher chamber pressure and presumably faster bolt carrier speed would require less extractor tension.
I could very well be mistaken.

I thought 300 blk had the same chamber pressure as .223 which is less than 5.56?

Peak chamber pressure has very little to do with extraction effort or carrier velocity.

Those are primarily determined by the shape of the cartridge's pressure curve and it's interaction with the gas system length, barrel length and the reciprocating mass.

[BC98]

I thought 300 blk had the same chamber pressure as .223 which is less than 5.56?

You're correct. Per SAAMI guidelines, max average pressure for 300 BLK and .223 are both 55,000 psi. Of course, this would only be for supersonic loads. Subs would be lower.

[Benito]

Hmm, I did not know that.

[GazillionUSMC]

Nice .300 blackout. I like that lower!

[Stengun]

Howdy MJDGator,

Nice build!

I'm a huge fan of the .300Blk and I like your build.

Your original barrel had a screwed up chamber in the shoulder/neck area. BA should have been honest about the barrel instead of claiming they didn't have an issue.

Paul