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Posted: 1/13/2019 9:41:11 AM EDT
[#1]
I haven't done a 12.5" barrel yet but have done a 13.3". I opened it up from .0625" to .0635" prematurely. It cycles 55gr Federal .223 with a Vltor A5H4. Depending on your buffer weight, you might be able to use the standard .0625" gas port. I definitely wouldn't jump all the way to .0670" if you have to make it bigger. I'd find a .0635" or 1.65mm first.
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Posted: 1/13/2019 10:59:21 AM EDT
[#2]
You want less gas with a suppressor, so I would start with what you have to see if you can set up spring and buffer for reliable function as is.
Step up gas port size only if you can’t get the rifle to run reliably, with minimal steps until you get reliability. It helps if your willing to limit your ammo choices to 5.56 or hotter 223 ammo when shooting unsuppressed. With a suppressor the cheap low power stuff will function. |
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Posted: 1/13/2019 5:50:22 PM EDT
[#3]
Yea I pretty much only shoot M855......going
To run carbine gas system and was thinking H buffer |
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Posted: 1/13/2019 9:45:30 PM EDT
[#4]
Colt spec for 16" carbine gas is .062".
There's no milspec for a 12.5" barrel, but the most consistent industry "standard" is .078". Some companies have been going smaller for smoother operation and for suppressed use. |
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Posted: 1/13/2019 9:51:26 PM EDT
[#5]
Quote HistoryQuoted:
Colt spec for 16" carbine gas is .062". There's no milspec for a 12.5" barrel, but the most consistent industry "standard" is .078". Some companies have been going smaller for smoother operation and for suppressed use. |
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Posted: 1/13/2019 11:34:16 PM EDT
[#6]
Quote HistoryQuoted:
That's way too big. If the 10.3" is .0700", how in the world would the 12.5" be 25% larger? Quote HistoryQuoted:
Quoted:
Colt spec for 16" carbine gas is .062". There's no milspec for a 12.5" barrel, but the most consistent industry "standard" is .078". Some companies have been going smaller for smoother operation and for suppressed use. A lot of companies are finally going smaller on the short barrel gas ports. FWIW, the Crane MK18 spec is .071", yet the Colt Commando with longer 11.5" barrel is .076", so it's not exactly uncommon in the industry. Especially considering the non-standard ammunition in the commercial market. |
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Posted: 1/14/2019 10:44:01 AM EDT
[#7]
Threw this quick spreadsheet together a while back - bounded between 14.5" at 0.0625" and 11.5" at 0.0700" known gas port sizes, and delineated in 1/10" barrel length increments. Was trying to decide what the proper GP size would be for a 13.8" barrel - but I gave up on the math for looking at the pressure curve change (meaning this list is linear and not correct, except for the top / bottom). So I just decided to stick with 0.0625" to start and then test, only open up further if needed.
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Posted: 1/14/2019 5:11:00 PM EDT
[#8]
Sons Of Liberty Gunworks uses .070" gas pets on their 12.5" barrels. As a company, they seem pretty obsessed with correct port sizing.
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Posted: 1/16/2019 4:44:10 AM EDT
[#9]
I'd go 0.063.
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