300 BLK w rifle length gas

S

Sgt_Jamez

Sergeant
Full Member
Minuteman
Dec 24, 2009
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Carmichael, CA
#1
I am a BLK noob, and I've ordered an 18" barrel with a rifle length gas system. After doing some more reading, it seems that H110/W296 might be too fast for a rifle length gas port.

Is this true?

I ordered the barrel from Black Hole Weaponry and they offer the 18" in a mid length as well.

Should I change my order to a mid length gas? Any thoughts would be appreciated!
 
#2
Re: 300 BLK w rifle length gas

<span style="font-size: 14pt"><span style="color: #000099">Sir,

I got my 16" barrel from Wilson and it's a carbine length system. It runs/groups great with H110 and 110gr V-Max bullets. I load them w/21.4gr of H110 and load long to 2.089" OAL. Brad from Selph Arms posted that load info on another board and he is definately right on for that load, at least for my rifle. Last but not least, you'll probably need to use an H2 or H3 buffer.

Matt
</span></span>
 
#3
Re: 300 BLK w rifle length gas

I'm still trying to understand the relationship of powder speed vs pressure impulse.

As I understand it... H110 has a high pressure impulse that falls off rapidly. Thus needing a shorter length gas system.

If that is true, wouldn't there be less pressure to cycle the bolt with a longer system (rifle length in my case). I don't understand how your advice of using a heavier buffer would address my issue.


Again, I am still trying to understand the nuances of the gas system. I am trying to figure out if I should have ordered differently and need to make a change while there's still time.
 
#4
Re: 300 BLK w rifle length gas

Sir,

Sorry, I wasn't clear. The heavy buffer was for the carbine length gas system. Your barrel was the 1st I'd heard of using a rifle length for the Blackout. I'm still learning as well but I don't see any advantage to a rifle length system in this caliber. Hopefully some other guys will add too this as well.

Matt
 
#5
Re: 300 BLK w rifle length gas

For optimum performance you should choose between sub sonic ammo or super sonic. The same gas port has a hard time handling both - optimally. Best results will come from dedicating the rifle one way or the other.

I have a 16" with pistol length gas. Super quiet, clean, reliable, and accurate with subs and fast powder.

But pistol gas will suck with super sonic ammo. Fast powder probably will not cycle with a carbine or rifle gas. An 18" with rifle gas is a terrible set up for subs, but it is probably just fine with super sonic.

edited to add: I would NEVER get a rifle length gas port in a barrel chambered for 300 Black
 
#6
Re: 300 BLK w rifle length gas

I can't do a can here in CA so it will definitely be a supersonic dedicated barrel.

The only 2 choices for the barrel in 18" was mid and rifle length. I hadn't properly educated myself before placing the order last week. BHW has a 6-8 week lead time. I still have time to alter my order, but I am now wondering if there's no advantage to an 18" barrel. Maybe best just to shift to a a 16" carbine length?

Also... 1:8.5" or 1:11" for 110gr-155gr slugs? (all supersonic)
 
#7
Re: 300 BLK w rifle length gas

why not call CMMG and get a 16" in pistol or look around for a 16" in carbine? there are quite a few that will make you this barrel in either pistol or carbine for right at or under $200
 
#8
Re: 300 BLK w rifle length gas

We made some 20 inch barrels with rifle length gas, and they did not work at all. I recommend you change the 18 inch barrel to a carbine length gas. Even mid length would have almost no chance of working - even with only full power ammo.

Before we sell a new barrel or upper configuration, we make a bunch and shoot thousands of rounds in each one. They are tested on high speed video, and we have shot over 100,000 rounds so far and learned from that. Here is the AAC 16 inch:

http://www.midwayusa.com/viewproduct/?productnumber=856314

This is in stock at Midway, and they ship same-day.

As for twist - any is fine. 1:6, 1:7, 1:8, 1:10, 1:12. There has been no evidence that 1:8 does any harm to supersonic. We have factory test barrels shooting 0.85 inch groups even with a 50 round averages (10 groups of 5 rounds each) in 1:8 and 110 grain bullets.

 
#9
Re: 300 BLK w rifle length gas

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body">I have a 16" with pistol length gas. Super quiet, clean, reliable, and accurate with subs and fast powder.

But pistol gas will suck with super sonic ammo.</div></div>

While I prefer carbine gas for barrels 16 inches and over, pistol gas does not suck - as long as the gas port is not oversized.

If you like carbine gas on a 16 inch 5.56mm AR, then you should like pistol gas on a 300 BLK. If you like mid-length gas on a 16 inch 5.56mm AR, then you should like carbine gas on a 300 BLK.

If you buy the barrel from the wrong company who did not do high speed video and cyclic rate tests with current ammo - such as Remington, it may be gassed for older Whisper(R) loads and then may be over gassed for the latest generation of ammo from Remington and others.
 
#10
Re: 300 BLK w rifle length gas

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rsilvers</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body">I have a 16" with pistol length gas. Super quiet, clean, reliable, and accurate with subs and fast powder.

But pistol gas will suck with super sonic ammo.</div></div>
...pistol gas does not suck - as long as the gas port is not oversized... </div></div>

Yes, it does. It is not just the port size or volume of gas...it is also the timing. Not saying it can't be done but it does suck for super sonic.

If super sonic only then stick with carbine gas.
 
#11
Re: 300 BLK w rifle length gas

Wow great info. I cancelled the BHW barrel and I will go with a 16" carbine. I definitely like the AAC barrel but @ $420 it's outside what I have to spend. I'll probably go with the CMMG. $200 and in stock.
 
#12
Re: 300 BLK w rifle length gas

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rsilvers</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dieselten</div><div class="ubbcode-body">I have a 16" with pistol length gas. Super quiet, clean, reliable, and accurate with subs and fast powder.

But pistol gas will suck with super sonic ammo.</div></div>
...pistol gas does not suck - as long as the gas port is not oversized... </div></div>

Yes, it does. It is not just the port size or volume of gas...it is also the timing. Not saying it can't be done but it does suck for super sonic.

If super sonic only then stick with carbine gas. </div></div>

I would stick with carbine gas even for subsonic 16 inch. But for short barrels, I am not sure carbine gas would be in spec.
 
#13
Re: 300 BLK w rifle length gas

I am pretty sure CMMG is only pistol gas. Again, I personally don't think that is a big problem, provided the gas port has been well selected - though I prefer the longest gas which works in spec for bolt velocity, and that is carbine. If you get it, and the rifle is cycling with too much energy, then try an H3 buffer (look for a 160 gram one).
 
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