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POOR_MAN
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Posted: 5/23/2012 2:10:31 PM EST
Just out of curiosity, does anyone have any idea what the common gas port size on a 16" barrel with midlength gas system in 5.56?

Thanks
bp7178
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Posted: 5/23/2012 2:17:59 PM EST
I'd go with .085", the same Wilson Combat uses on their barrels.

I wouldn't go smaller unless you were set on running 5.56mm ammo and a light(er) buffer.
BSWilson
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Posted: 5/23/2012 2:20:43 PM EST
[Last Edit: 5/23/2012 3:16:16 PM EST by BSWilson]
.064" IIRC for 14.5 carbines & 16" midlengths (.750" dia block) for 5.56 pressure ammo.
JmPnTX
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Posted: 5/24/2012 9:40:29 AM EST
[Last Edit: 5/24/2012 6:36:39 PM EST by JmPnTX]
I have two 16" mid-length barrels, each with a 0.750 barrel diameter at the gas block. The barrels are from different makers and have port dimensions of 0.075" and 0.085". I've also checked with a third vendor, just to compare against my barrels and they came back with 0.076" for what they sell. The 0.085" port barrel feels overgassed to me. Harder recoil than my 16" carbines (Spikes - 0.068") and I am running an ST-T2 buffer and auto BCG on both of the middies. On the 0.085" ported barrel I'm even running an AAC brakeout and it still has more recoil.

Keep in mind that from 0.075 and 0.085 is about a 28% increase in port area...

0.084" port is what I've also seen spec'd for a 14.5" barrel, mid-length.
wrighteouskill
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Posted: 5/24/2012 10:07:25 AM EST
depends on contour of barrel. if its a bull it needs to be larger b/c the gas has a longer distance to travel through the metal as opposed to a lightweight. do you get it? if not lemme know and i can explain further.
Direct-Drive
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Posted: 5/24/2012 12:14:09 PM EST
I've seen Colt listed at .062 - .063 (full power ammo) for 14.5 - 16
Builders for the civvie market will sometimes go .068 - .073 not wanting call backs for failing to cycle cheap, low pressure ammo.
wyv3rn
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Posted: 5/24/2012 12:16:58 PM EST
[Last Edit: 5/24/2012 12:24:15 PM EST by wyv3rn]
The answers are already here, but I will chime in to confirm. As stated by others it depends on barrel diameter/profile at the gas port. For 16" middy with .750" profile at the gas port the gas port size is .075" - .085". Yes, .085" is on the large end. .075"-.080" is a good starting point for a new 16" midlength (.750" profile under the gas block) barrel. You want the smallest size you can get that will still lock the bolt back reliably with an M16 carrier, H2 buffer and low pressure .223 ammunition (ex. Wolf) with no lube (not advocating no lube for "normal use", just in this step of manufacture). Remember gas port erosion will increase flow over time. For a point of reference most Sabre Defence 16" Midlengths shipped with .080"-.082" gas port.
badazzar15
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Posted: 5/24/2012 8:23:06 PM EST
Go with .076"-.082".

.085" will be over gassed even with an H buffer.
Tom Miller (CEO)
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badazzar15
Spike's Tactical
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Posted: 5/24/2012 8:24:51 PM EST
Originally Posted By wrighteouskill:
depends on contour of barrel. if its a bull it needs to be larger b/c the gas has a longer distance to travel through the metal as opposed to a lightweight. do you get it? if not lemme know and i can explain further.


Pig tail gas tubes also increased the distance that gas had to travel and they didn't do a damn thing.

Tom Miller (CEO)
website: www.spikestactical.com
company email: sales@spikestactical.com
my personal email: acreativebuilder@aol.com
phone: 407.928.2666 (ext. 105)
fax: 866-283-2215
EzGoingKev
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Posted: 5/25/2012 1:59:54 AM EST
Originally Posted By Direct-Drive:
I've seen Colt listed at .062 - .063 (full power ammo) for 14.5 - 16

That would be for a carbine length gas system as Colt does not produce rifles with mid-length gas systems.

Using a pin gauge that was then verified with a micrometer I measured .072" on my mid-length Daniel Defense lightweight profile barrel.

Direct-Drive
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Posted: 5/25/2012 6:58:23 AM EST
Originally Posted By EzGoingKev:
Originally Posted By Direct-Drive:
I've seen Colt listed at .062 - .063 (full power ammo) for 14.5 - 16

That would be for a carbine length gas system as Colt does not produce rifles with mid-length gas systems.

Using a pin gauge that was then verified with a micrometer I measured .072" on my mid-length Daniel Defense lightweight profile barrel.


Never said mid-length.
Colts civilian offerings in 16" are carbine gassed.
Tim_W
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Posted: 5/25/2012 8:47:03 AM EST
Originally Posted By POOR_MAN:
Just out of curiosity, does anyone have any idea what the common gas port size on a 16" barrel with midlength gas system in 5.56?

Thanks

.081 for a mid length 16" barrel.
contour of the barrel does not matter only the size of the barrel under the gas block.

EzGoingKev
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Posted: 5/27/2012 7:53:22 AM EST
Originally Posted By Direct-Drive:
Never said mid-length.
Colts civilian offerings in 16" are carbine gassed.

So the OP asked specifically about the size of gas port for a mid-length gas system and you purposely gave him bad info?

I am not trying to start shit, but why would you even post those specs?
Direct-Drive
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Posted: 5/27/2012 8:00:29 AM EST
Originally Posted By EzGoingKev:
Originally Posted By Direct-Drive:
Never said mid-length.
Colts civilian offerings in 16" are carbine gassed.

So the OP asked specifically about the size of gas port for a mid-length gas system and you purposely gave him bad info?

I am not trying to start shit, but why would you even post those specs?

Nevermind.
Russ4777
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Posted: 5/27/2012 8:16:26 AM EST
Just measured one of my Model 1 Sales barrels at 0.078".
1st Cav Div, B 5/7
Vietnam/Cambodia
1970
N2CH_556
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Posted: 5/27/2012 9:22:46 AM EST
[Last Edit: 5/27/2012 9:30:15 AM EST by N2CH_556]
Originally Posted By POOR_MAN:
Just out of curiosity, does anyone have any idea what the common gas port size on a 16" barrel with midlength gas system in 5.56?

Thanks


ETA: nevermind... missed the midlength requirement... ask DD or BCM

http://bit.ly/Jv1o7z

http://www.ar15.com/archive/topic.html?b=3&f=66&t=564962


16" barrel, .625" dia., 8.375" from muzzle;
Port sizes from .063" to 078"
16" barrel, .750" dia., 8.375" from muzzle;
Port sizes from .070" to .086"