Ar gas length, longer barrels

Blutroop

Sergeant of the Hide
Oct 25, 2018
136
106
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Alaska
#1
I’m working on a 27” barrel for a ar in 17 Remington. It’s taking a lot longer than it should but I don’t have all the nice fancy tools either. Anyways I started thinking and comparing different lengths of barrel vs gas system and came to the conclusion that a standard rifle length gas system might be way to short for a 27 barrel. I want this to be smooth and not beat itself to death. Has anyone experimented with this? I was thinking of getting all super scientific and stretch it out to 20 then start lightening bcg, buffer, springs till I got it to function (if it wasn’t already) have anyone blazed this trail for me? Can anyone claim it won’t work and give a decent argument why?
 
Apr 8, 2006
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S.E. PA
#2
Go +2 and run an adjustable gas block. I prefer Superlative Arms Gas Bleed block. I run a light weight carrier and solid delrin buffer. Tune gas block to lock the bolt back on an empty mag + 2 clicks. Super smooth and no issues. Start with a .085-.090 gas port size and go from there.
 

GH41

Sergeant
Mar 18, 2014
444
18
18
#3
Here is my argument.... Shilen make and sells a 24" 17 Remington barrel running on a rifle gas port. Rifle gas length is 12". Shilen can make anything they want. I cannot imagine them building something that doesn't work.
 

Blutroop

Sergeant of the Hide
Oct 25, 2018
136
106
43
Alaska
#5
Go +2 and run an adjustable gas block. I prefer Superlative Arms Gas Bleed block. I run a light weight carrier and solid delrin buffer. Tune gas block to lock the bolt back on an empty mag + 2 clicks. Super smooth and no issues. Start with a .085-.090 gas port size and go from there.
Tell me more about your lightweight carrier please
 
Apr 8, 2006
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S.E. PA
#6
I have a 24" 223 with a rifle gas system. A 26" CLE 223 with +2. A Seekins 18" with rifle gas.

White Oak stocks a 26" 223 with a +2 gas.

Blutroop was asking for options. My only concern is 17Rem has less gas volume. But with the gas port size, adjustable gas block, light weight carrier and lightweight buffer it should run super smooth.
 

Niles Coyote

Gunny Sergeant
Aug 13, 2007
3,945
318
83
South West, MI
#7
On a 27" barrel IDK on gas system length but I'd start with a small port size and keep opening it up till it works with the Powder and load range you will be using. No sense using an adjustable gas block when you have it in your power to make it correctly for your needs.
 
Likes: Eagle1899

XLR308

Sergeant of the Hide
Mar 22, 2018
1,227
903
113
Grand Junction, Colorado
#11
Agree on the light weight carrier and buffer, the adjustable gas block is just a bonus to complement the lowered operating mass and fine tune everything based on what load recipe you settle on.

They are spendy but I really like the JP nitride low mass carrier and LMOS buffer I am running with a SYRAK adjustable block. Think I will acquire one of the Brownells ones for future project.

For a barrel that long I think I would personally go with a +2" gas system.
 
Jun 21, 2009
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Barren plains of Kansas
#12
Ok, correct me if i am wrong, and I probably am cause I'm not a AR expert or a gunsmith, but with a 17 you are dealing with lower gas volume at high pressure. So by stretching the gas length you are lowering the pressure or atleast the dwell time of pressure before the bullet exits the bore. But by using light springs and buffer you are making the pressure appear higher to the operating system. So why not leave it at rifle length and run the standard bcg and buffer and adjust the system with a gas block? Please educate me on this.
 

XLR308

Sergeant of the Hide
Mar 22, 2018
1,227
903
113
Grand Junction, Colorado
#13
By reducing the bore diameter from 22 to 17 you really aren't working with less volume all though the 17 rem case has the shoulder pushed back slightly the reduced bore diameter is making up for that.
 
Apr 8, 2006
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18
S.E. PA
#14
Longer gas system in itself bleeds off gas at lower pressure point in the barrel farther from the carrier. This does two things. Bolt remains locked longer and the force unlocking it lower. Chamber pressure drops before unlocking = more cartridge dwell time in the chamber after firing. Lower unlocking speed of the carrier = the rifle moves less. Going to light weight carrier with a longer gas system and an adjustable gas block allows the rifle to be tuned for longer dwell time before the carrier unlocks (easier on brass) and a very light recoil impulse.
 
Jun 21, 2009
132
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Barren plains of Kansas
#15
So your not tuning to try to make it reliable your fine tuning to improve recoil pulse and bolt dwell. I was under the incorrect assumption that the question was to get reliable extraction. Thabk you for the clarification and I will sit back and learn shit now.
 
Apr 8, 2006
397
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18
S.E. PA
#16
No worries.

Reliable extraction is a benefit of all this. The longer the dwell time before the carrier begins to unlock the bolt allows the chamber pressure to drop and extraction to be easier.

On the flip side a heavy buffer holds the carrier in place longer (more mass) and does the same thing. I like heavy buffers on large format AR's and SBR's with Suppressors.
 

GH41

Sergeant
Mar 18, 2014
444
18
18
#17
"I’m going off memory here but isn’t rifle length 15 "

12" measured from the bolt face. 13 and change measured from the rear of the barrel extension. Gas length is measured just like barrel length... From the face of the closed bolt.
 
Apr 8, 2006
397
8
18
S.E. PA
#18
"I’m going off memory here but isn’t rifle length 15 "

12" measured from the bolt face. 13 and change measured from the rear of the barrel extension. Gas length is measured just like barrel length... From the face of the closed bolt.
Gas tube length for rifle is 15"
 
Apr 8, 2006
397
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18
S.E. PA
#20
15.125" is the length of a rifle gas tube.

Rifle length gas is 12.625" from back edge of extension shoulder. Gas journal shoulder to extension shoulder should be 12.125".
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,171
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Lebanon, Missouri
#21
Look up "Dwell time", it refers to the time the bullet is in the barrel AFTER the gas port.
You won't have any gas PRESSURE issues, but you may have VOLUME issues.
Use a +2 or better yet a +3" gas tube and an AGB, as all the others have said. With a barrel that long, you will be uncorking it really late and may have some odd issues with a shorter gas tube.
 

Blutroop

Sergeant of the Hide
Oct 25, 2018
136
106
43
Alaska
#22
I ordered a +3, adjustable gas block, and brownells lightweight nickel boron carrier. I still wanna find a lightweight buffer and spring. I will let everyone know how it works out. Thanks for all the responses.
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,171
10
38
50
Lebanon, Missouri
#24
If you have a punch and small hammer, just knock out the roll pin in a regular buffer, take out the guts and put it back together empty.
If you are not running full auto or a binary trigger, it will work as a lightweight buffer. (better than a solid delrin one).

Buy a Tubb spring, and look up my old posts on the Ultimate AR, and it will give you instructions on cutting the spring down properly.
 
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