Starting a 300 Blackout Build

[MarcSpaz]

Well guys and gals, I hope you don't think less of me... but I bought a complete upper today. I just could not find quality parts to assemble my own without spending more than a complete AAC upper. So, I just bought the complete AAC 9" upper.

It's still pretty cool though. I'm going to fire off a few pics later and I will post them up.

Oh, and don't wast your time with PMags for this round. I'll explain later, when I post the photos. It will be easier once you "see" what I mean.

[bryanrheem]

Definitely don't think less of you, especially because that's exactly what I plan on doing!!! Where did you buy your upper if you don't mind sharing? I've been looking here and there, trying to find a great deal (used/new). Did you get one with the new bolt?

I am also VERY curious about Pmags as I was def. planning on using them as well!

[jdonovan]

The central rib in the pmags can be a problem depending on the nose of the bullet you use.

I find the GI style mags work better for my 458, and 300 blk.

[MarcSpaz]

Definitely don't think less of you, especially because that's exactly what I plan on doing!!! Where did you buy your upper if you don't mind sharing? I've been looking here and there, trying to find a great deal (used/new). Did you get one with the new bolt?

I looked everywhere. I couldn't find anyone willing to sell an AAC for any less than MSRP. So, I just picked it up from my regular shop, Virginia Arms. He is a direct distributor, so I asked him to order it Monday and I got it today.

I am not sure how to tell which bolt I have... new or old. Was there an issue with the older version? I am assuming that because its new hardware straight from AAC, that its the latest version.

I am also VERY curious about Pmags as I was def. planning on using them as well!

JD nailed it. There is a rib that runs all the way down the mag on both sides. In the PMag, it seems to be dual purposed. It is used to guide the floor plate and keep the ammo properly aligned in the mag.

If you look at the picture below, you can see that the guide presses on the neck of the .223 cartridge. However, on the .300, it presses on the projectile. The .300 projectile is obviously a touch wider than the neck of the .223. On the PMag, the mag swells or bulges due to the ammo forcing the plastic to give, rather than the plastic properly aligning the ammo. The GI mags don't bulge, but instead push the ammo into place.



I wont try firing it. The loaded mag would barely fit in the mag well and the mag catch would latch, but it was questionable at best, as to if it did latch. I figured I would have feed problems if I tried to send rounds down range. Just doesn't seem safe.

I put my laser/light combo on it and added some flip-up backup sights. Here are a few pics...

Bolt Carrier Group



AAC Upper.



Knights Armament Co. URX handguard. Full rail on top with short rails at the front on the sides and bottom. The holes on the sides are threaded for mounting accessories.



Complete Upper



Connected to the lower...

[bryanrheem]

Yes, that new bolt is nickel boron coated. I've seen a lot of uppers (used) with the old bolt, but since you bought it new, you're good to go!

have you investigated other mags like Hex mags? I wonder if there are other options… too bad because I was buying OD green pmags specifically for this round to avoid confusion.

Are you planning on reloading? Round availability seems to come and go. You just now need a nice 30 cal can to thread on that nice FH.

[jdonovan]

have you investigated other mags like Hex mags? I wonder if there are other options… too bad because I was buying OD green pmags specifically for this round to avoid confusion.

the troy battle mags seem to work ok.

You can use pmags, you just have to file down the ribs a bit.

[MarcSpaz]

Yes, that new bolt is nickel boron coated. I've seen a lot of uppers (used) with the old bolt, but since you bought it new, you're good to go!

That plating caught my attention quick. A.D.D. + Shiny = Squirrel!

Don't know what the benefits are though. Have to look into it.

have you investigated other mags like Hex mags? I wonder if there are other options… too bad because I was buying OD green pmags specifically for this round to avoid confusion.

Not really. I have been recently buying the metal mags for $10 each. I'll just go get a couple more on payday. LOL There isn't much weight saving with the polymer mags. 30 rounds of .300 ammo is pretty darn heavy anyway. I figure I'll stick with the metal mags.

Are you planning on reloading? Round availability seems to come and go. You just now need a nice 30 cal can to thread on that nice FH.

I am planning on reloading now. No way I am going to spend $1.30 to $1.90 per round for very long.

And yes, a can is in the works.

the troy battle mags seem to work ok.

You can use pmags, you just have to file down the ribs a bit.

Are you taking them apart to do that? Like... splitting the halves?

I was going to keep them for range trips with .223 / 5.56 and just use metal for the 300. Maybe I can clean a few of the PMags up too.

[jdonovan]

Are you taking them apart to do that? Like... splitting the halves?

with $7 mags that work... i've found no reason to screw with modding pmags... but some people have an irrational attachment to them, and must use them at all times.

[MarcSpaz]

Hahaha. I hear you there. I really don't want to "wonder" if its going to work.

I am just finding it a little hard to toss 7 PMags in the trash when they seem to work okay with 5.56. I don't plan on being in a hunt or defense situation with these mags. That's for sure. Range trips are as far out of the locker those PMags are going.

[ Post made via Mobile Device ]

[0ne5hot]

Nice setup Marc.
I finally got around to posting up my 300blkout build.
http://vagunforum.net/your-hardware/pistol-t22838.html

Also, what Gen Pmags are you using? I am using the new Gen3 40 round Pmags with Sierra 220 grain MatchKings and they do not seem to have the problems you were describing.

[MarcSpaz]

Thanks Brian!

I'm not sure how to tell. I bought them about 2.5 years ago. Is there a way I can ID what gen they are?

[0ne5hot]

The gen 2-3 Pmags in my stash have Gen2 or Gen3 marked on them somewhere it seems to change depending on the manufacture time.

[MarcSpaz]

I took my 300 blackout to the range today. OMG is that thing awesome! I had such a fun time shooting this weapon. I wish I had this years ago.

What blows my mind is, its a 7.62/.308 projectile in a .223 case, with more energy than a 5.56, but makes such little noise that I can shoot it out of a 9" barrel without hearing protection and not having my ears ring. It defies all of my preconceived notions. LOL

[MarcSpaz]

...Also, what Gen Pmags are you using? ...

Just checked.... I had the same problem with my Gen 1's, 2's and 3's.

[jdonovan]

I with more energy than a 5.56, but makes such little noise that I can shoot it out of a 9" barrel without hearing protection and not having my ears ring.

suppressed, or just subsonics?

[MarcSpaz]

Don't have a can yet. I was just using subsonics. I was really surprised though. Even without the can, it's not as loud as my 40 S&W.

[MarcSpaz]

Quick question for those in the know... while shopping for over the counter range ammo I am getting the impression that unless it is labelled subsonic, it's supersonic. Is that right?

I think I remember reading that 208 and 220 grain is always subsonic, but 147 - 145 grain or less, is always supersonic. Short of looking up the stats before I buy, I have no idea what I can trust other than if labelled subsonic.

[jdonovan]

What blows my mind is, its a 7.62/.308 projectile in a .223 case, with more energy than a 5.56, but makes such little noise that

I was just using subsonics.

subsonics are only about 500 ft-lbs of energy. Handgun class power. Nothing to write home about.

Supersonics, 1400 for the BLK, and 1750 for the 5.56. 5.56 is still the winner for energy.

When you get to short barrels, then you get an energy advantage to the 300 blk, but most of the supersonic ammo on the market expands poorly at the reduced velocity that a 9" bbl generates.

Even the 110 gr black tip from barnes needs 1300 FPS impact velocity to get some expansion, and out of a 9", its already starting at 1100.

I can shoot it out of a 9" barrel without hearing protection and not having my ears ring.

a subsonic 220gr is still above 150db. Don't think the lack of ear-ring is a pass on hearing damage. You ARE harming your hearing without hearing protection.

I think I remember reading that 220 grain is always subsonic, but 145 or 147 grain is always supersonic. Short of looking up the stats before I buy, I have no idea what I can trust other than if labelled subsonic

I've never seen commercial 220s that were not subsonic, nor have I seen < 150's that were not supersonic. YMMV =)

[MarcSpaz]

I was going to stick to the subsonic rounds. I read some 300 BLK predator rounds at close range expand as much as 200%+. Even at handgun energy... I figure that will be fine for home protection, which was the main reason for the build.