.300 Blackout Upper Build

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Aqualung

Aqualung

Blackhawk
Joined
Mar 17, 2005
Messages
898
City & State/Province
Philadelphia, PA, USA
I built this upper for my AR556, this upper to give myself a little caliber variety.

Here's the finished upper:


Here it is on my AR556 lower:


Parts list:
Anderson stripped upper receiver
AR Stoner barrel in .300 AAC Blackout, 1:8 twist, pistol-length gas system
Microbest BCG
Yankee Hill SLR Slant Series Keymod handguard (Spectre-length)
Yankee Hill ejection port cover
Locally-manufactured low-profile gas block
Noveske pistol-length gas tube
DPMS A2 muzzle device
Anderson charging handle
BCM and generic rail and Keymod slot covers in FDE.

This is my first build and I made some rookie mistakes, but nothing that had a permanent effect.

Then, I got an "advisor" that made sure I was doing things right:


I finished building it last night. I figure I'll mount my Bushnell AR series 1x4 scope letter this weekend.

Aqualung
 
You will like the 300blk, just be sure to keep things clearly marked so you won't mix the two. Like has been said, "what goes up, must come down", things that go in, must come out.
 
cwmoss1970 said:
You will like the 300blk, just be sure to keep things clearly marked so you won't mix the two. Like has been said, "what goes up, must come down", things that go in, must come out.
Click to expand...

Thanks. I'm planning on getting different color ammo boxes and the like.

And the Brother P-Touch is my friend :D

I've already read the horror stories of folks firing .300 BLK out of 5.56 uppers (or not, as the case may be...).

Aqualung
 
This thread got changed, as I ponied up a few Cabela's gift cards and Cabelas Points to build a lower for the .300 Blackout project.

Here's the final rifle:




And for those paying attention who are saying "it doesn't look any different than the AR556 lower", I decided I wanted to go "Back in Black" with the AR556, as tricking it out with FDE didn't give me the results I wanted...


- Spikes lower
- Bushmaster LPK except for springs and trigger guard
- JP yellow springs
- Magpul enhanced trigger guard
- ATI buffer tube
- Magpul SL stock and grip in FDE
- Magpul BAD Lever

Now, just need to get to the range...

Aqualung
 
Finally got the rifle to the range tonight.

I set the target at 50 yards and put in my laser boresighter. Dialed it in and then loaded up the mags.

I lined up and squeezed off 5 rounds. I couldn't believe what I saw in my spotting scope:


I proceeded to take a bunch more shots and I'm sold on the .300 Blackout:


Even at 100yards, the groups opened up, but still stayed in the plate.

I was shooting Remington 120gr fmj.

I then tried some Firocchi 150gr and it grouped about 3"-4" low at 50 yards.

I think the 120gr is this rifle's sweet spot. I've got some Hornady 125gr SST bullets that I'll be loading to try.

Downside, I think it's short-stroking a bit, as it tosses brass at about 5:00, dings them off the deflector to leave a brass smear and dents the case mouths pretty good. However, I can live with it.

Other good news from the range. Got the UTG carry handle/sight dialed in on my AR556, and the Single-Six Convertable I just bought shot like a dream with both cylinders. Overall, a good day at the range.

Aqualung
 
Change the buffer spring will help the troubles you got denting case and were the throw out.
If you have a pistol gas system go with a 10 1/2 spring not a 11".
 
JOHNNY WACKO said:
Change the buffer spring will help the troubles you got denting case and were the throw out.
If you have a pistol gas system go with a 10 1/2 spring not a 11".
Click to expand...

It is pistol-length. I guess I can trim off some coils?

Maybe I'll buy another spring and cut that one down.

Thanks.

Aqualung
 
what buffer tube are you using? I have bought different springs that are the same size but different pressure .There are mill spec tubes and commercial tubes also. you tell by 1 has a flat end and 1 is angle end tube.flat is mil spec I THINK.
my 300 anderson build has a colt open bottom(lighter) bolt carrier for light loads(sub sonic). it is cut open on the hole bottom no strap at the end.
at a few bucks on ebay i bought several springs and swopped then out till 1 worked.
most times when you dent the case it means the bolt is moving back to slow or out of time.and the next round coming up and is hitting the empty 1.
is your bolt carrier chromed were the head goes in ? I soak my bolt in oil for a day even if andersons said no lube needed.They make a gas tube called a pig tail for pistol gas systens that coils around the barrel to make it longer and increase pressure also.when i was building 1 a week i had 4 or more springs and tested till 1 worked ok. they are like $4 on ebay. go to several dealers and get then ,they will be different .I run a 10" pistol 300 with a KAK tube and the shockwave brace-fin.with a 10 1/2 spring.but the KAK tube is longer then a pistol tube and lightens up the pressure of the spring .
try wiring up the first couple coils of the spring with a zip tie to make it shorter before cutting anything.
if a spring is to weak it wont hold the bolt shut tight enough and you loose accuracy.The spring works both ways.so watch that.
a pistol system lets the gas out sooner but the pressure is less meaning the case don't have time to expand and seal in the chamber enough and you loose gas pressure around the brass case end.some barrels have a bit bigger hole to let more gas out.my 101/2" 762x39 barrel has a pistol gas port but the hole is made bigger.
pull your gas block back off look at the powder burn marks and see if they are lined up even too
I built a 223 that took over 100 rds before it started to work rite. I try to stay with carbine gas systems myself.
 
It's a milspec tube. Flat back is milspec, angled is commercial.

I was going to put on a pigtail gas tube, but my free-float handguard didn't allow enough clearance.

My BCG is a full-auto, pretty heavy. I also realized it was a bit dry when I tested it, so that may have contributed (strangely enough...thought I'd lubed it up pretty well before going to the range).

As I'll be mostly reloading for this, I'll see how my loads behave as well. I'll also try the zip-tie trick you mentioned.

Thank you.

Aqualung
 
It mite work it's self out as you brake it in.I like to run 100 rds through before i start changing things unless it is jamming. Good luck hope i helped. :D :D
 
Not sure what sort of sights you're actually using, you should be getting cloverleaf holes with the right ammo.
You may find the need for an adjustable gas block to control the violent extraction/ejection of super sonics with the pistol gas.
I assembled a good performing 300 using a Red-X 16" w/carbine gas w/adjustable block that shoots 110-208 grain bullets quite well and can be fine tuned to toss cases anywhere from 2 to 5 o'clock.
 
He has a pistol gas system,I feel you loose gas at the breach do to case not expanded tight to bore before it goes out the pistol hole. they do make different size holes to help this.just what i think others may not??

i was thinking of swapping the barrel out on this to 300bo.
it's my last build and i went with fde and it did not move like the others did.
 
How could you put a 300bo 30 cal bullet in a 223 /556 barrel thats a 22 cal.no way would it chamber the round in battery.it would not let the bolt shut let alone fire.now the other way around would chamber and fire but brass would most likely expand and get stuck in the chamber...
 
JOHNNY WACKO said:
bolt won't shut on a 300bo in a 223
Click to expand...
Wanna bet
http://www.guns.com/2014/03/11/photo-day-happens-shoot-300-blk-5-56-rifle/

http://www.300blktalk.com/forum/viewtopic.php?f=128&t=99797
 
If the BO bullet was one of the 125gr spire point ones frequently used in supersonic loads, it would be a matter a seating depth and neck tension. Since the springs are working the bolt, you'd probably not notice until it was too late.
 
I GUESS ANYTHING IS POSSIBLE UNDER FORCE AND STUPIDLY.

thats a 220 gr sub sonic rd in my picture

lets not forget everything on the net is true nothing is fake or wrong.

If you can not tell the difference between these 2 rounds you should''t own a rifle at all. there so different looking

and i think the bolt would just blow open before the receiver blew up or the bullet stretch and go that far in to the barrel like that the 300 sub sonic dont have that much powder to do all that damage,
but stupid people could make stupid things happen like loading wrong powder or something like that.Now in a bolt action rifle were the bolt is locked maybe but a ar bolt is only held shut with 22lbs of spring and would just open up and release the pressure.and a 223 in a 300 would fire and not stick in the barrel at all like a 30/30 in a 32 special would.
and the 1 post said artificial head space on it'
you havent convinced me .

 
JOHNNY WACKO said:
How could you put a 300bo 30 cal bullet in a 223 /556 barrel thats a 22 cal.no way would it chamber the round in battery.it would not let the bolt shut let alone fire.now the other way around would chamber and fire but brass would most likely expand and get stuck in the chamber...
Click to expand...

If you compare the two rounds, the .300BLK case is quite a bit shorter, but could still chamber in a 5.56 chamber:


I haven't tried it, but it looks possible...I fanatically keep the rifles and ammo separate.

Edit: Sorry...didn't see there was a second page to this thread.

Aqualung
 
anything is possible and you should watch all your ammo not just these 2 calibers but i think the results are a bit over the top.not with a semi maybe with a bolt action.

but you have to keep all your ammo separated from each other,that's just common sense.
to keep you and mostly the people beside you safe t all times..
 
JOHNNY WACKO said:
How could you put a 300bo 30 cal bullet in a 223 /556 barrel thats a 22 cal.no way would it chamber the round in battery.it would not let the bolt shut let alone fire.now the other way around would chamber and fire but brass would most likely expand and get stuck in the chamber...
Click to expand...
There are a bunch of them

http://www.thefirearmblog.com/blog/2015/01/13/psa-always-known-caliber-300-blk-5-56-kaboom/

http://www.ar15.com/forums/t_3_121/575869_Can_you_shoot_300_BLK_out_of_a_223____Update__It_s_Out___Page_2.html

http://mygunculture.com/r-i-p-one-ar-15-rifle-another-300-blackout-223-kaboom/

https://sinistralrifleman.com/2015/01/03/300-blackout-in-223-kaboom/
 
If you force it hard enough it could happen but you cant blame the gun. That first post is bull in my book the pressure would not have been behind the bolt and blow the receiver but just the opposite.
and if you force it hard enough to get it in there your a dummy.you would have to use the forward assist and a rock or you made a loading mistake not the guns fault.
if it don't want to shut you check it out not force it.that is user error nothing to do with the gun or they built the rifle with junk parts.If you use a bolt group that has not been MPI you are taking a chance even with 223.there are lots of cheap bolts on the market that make the guns look bad when it should be the cheap guy's fault that bought the cheapest parts he could find then cry's the gun was the reason.
the bolt head has to be pressure tested or you are taking a chance what ever caliber it is.
It is people who don't know what there doing and think they do that are making these mistakes not the caliber of the ar.
every case there is user mistake,like blaming the car for a bad driver or mechanic..
but i do buy the red tip bullets for that reason too.
so the point is stupid mistakes by stupid people cause stupid accidents.
 
I made the mistake of letting a guy buy his own parts on my 4th or 5th rifle build. and he showed up with this chromed BCG that had no MPI stamped on the bolt head.I called him on it and he said i paid big money to get that chromed bolt it's a good 1 and i foolishly put it together and 2 weeks later he shows up with it stuck shut. well the bolt head split and jammed in the barrel feed ramp.He cried and tried to blame it on me even though i told him that MPI was a pressure test were the test it in over twice the pressure it will have to make sure it will hold up to any load the 223/556 has.
after that i won't build a rifle or pistol that i don't buy every part to be sure it is up to all specks.
You see these guys say i can buy a ar15 for 1/2 of what you want for your home made 1. But they don't understand there getting less then 1/2 the rifle i am selling them.If you buy 1 for less then $700 new you can figure your getting un tested parts that wont hold up to lots of shooting like the big dollar 1 do.
so those post you see are most likely cheap parts put together by guys that don't have no idea what is what and think they do.
i build all andersons but wont use a anderson bolt. i make sure i get the MPI tested BCG thats the key its the bolt and the piston all in 1 and the most under pressure part or at least 1 of them.
 
The effects of this mistake depend on the direction that the high pressure gases exit. There will be a weak point in the brass, if one is lucky it will be near the ejection port and make noise, if one is not it will deform the receiver.

You make several statements that indicate to me that you do not understand how an AR-15 is engineered to work:
-The bolt is not held shut by 22 pounds of spring pressure; it is held shut by a mechanical interference that is removed when the gas pressure moves the bolt carrier. If you obstructed the gas tube, the bolt would not move at all upon firing the rifle and would need to be manually cycled. Since the bullets in these incidents don't reach the gas port before the pressure ruptures the case, the only pressure release is case rupture.
-That 22 pounds of spring pressure can overcome the neck tension in cases where the bearing surface of the bullet is small, for instance, that 125gr bullet I pointed to earlier that just about fits in the chamber.
-Swaging bullets regularly takes tens of ksi and reductions are generally not on the order of .308 to .223 in a single step. Add to this the fact that the controlled explosion going on behind this swaging operation has a certain pressure curve that makes it safe versus just a bomb and it is not hard to understand how this operation could exceed the 70ksi flow stress of the brass case and cause an uncontrolled gas escape.
-Once the gas has escaped the case, the bolt will not hold the pressure in, no matter how high the pressure it has been tested at, because it is not a sealed system. This is not a quality of parts problem. It may be a quality of ammunition problem in combination with user error, but blaming cheap rifles indicates a lack of understanding about the issue here.
 
the 22 pounds is the pressure of the spring closing the bolt, any more would have to come from the assist being used to close the bolt.and the bolt will open even if there is no gas port in the barrel it will open from pressure.not enough to eject or work correct but will open enough do to pressure.and release pressure out the port.I found this out by trying to have a barrel made with no gas hole to make a bolt action style ar.The barrel maker saids the bolt will release even without a hole unless you release the gas some how else.

The issue is use the rite ammo in the rite gun rite.

There are slow motion videos of were if your spring is not holding the bolt tight enough the split second before the brass case seats in the chamber gas will escape around the brass and cause a bounce of the bolt.

in the 1 video the guy beating the bolt open after firing the 300 in the 223 is the bolt head split and stuck in the feed ramp were a good quietly bolt would have not split.

I am leaving it there i see by your profile you just like to argue about stuff. For all i know you don't even have or fired a ar in your life. so go argue with some 1 else i'm done here.
 
"The barrel maker said..." Sounds like you're not the only one who doesn't understand how an AR-15 works.

https://www.midwayusa.com/product/578769/noveske-switchblock-gas-block-clamp-on-ar-15-standard-barrel-750-inside-diameter-stainless-steel-black-nitride-for-223-556x45mm-carbine-length-gas-145-to-16-barrels

This product turns off the gas port to make the rifle a single shot, straight-pull rifle.
Product in use: https://www.youtube.com/watch?v=tPwGFpZV_BU

I would say most of my posts are thoughtful and well researched. I understand if you don't operate that way, but it's how I choose to operate as a science/engineering professional. I would suggest your aspersion on my general behavior is projection: https://en.wikipedia.org/wiki/Psychological_projection
 
Just don't be a dick and put the rite ammo in the rite gun and shut up about it.If you blow yourself up for that reason you got no 1 to blame but your own stupid self.
 
"How could you put a 300bo 30 cal bullet in a 223 /556 barrel thats a 22 cal.no way would it chamber the round in battery.it would not let the bolt shut let alone fire."

As simple as pushing the bullet back in the case, Mr. Wacko. I try to have my 300 loads pretty well compressed to prevent bullet set-back since none of the bullets I use have a crimp groove in the right place.
 
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