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Posted: 2/8/2010 4:15:16 PM EDT
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Ok, so this DC area snowmageddon or whatever they are calling it has led me to plan my build of a 5.56mm SPR. So the question I have is what is the best gas system length? I have seen intermediate as the best, but also rifle length. What do the experts truly say? Thanks
S/F |
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If you are talking about an 18" barrel, you will want either a midlength or rifle length gas system. A rifle length gas system will be a bit under gassed. A midlength gas system will be a bit over gassed. I believe most people use a rifle length gas system on 18" barrels. However, I chose a midlength on an 18" barrel for a couple of reasons.
1. My rifle length free float tube completely covers and protects my gas block. 2. It will be a pretty low round count rifle (match ammo is expensive); therefore, if there is extra wear an tear because of it being over gassed, it shouldn't really matter much. 3. Reliability in very dirty and/or cold environments should be higher because of the extra gas force. 4. It is already a heavy rifle (scope, scope mount, bipod, 18" heavy barrel, free float tube, etc.) that will be shot almost exclusively in the prone. Because of this, the slightly increased recoil shouldn't be as noticeable as in an over gassed KISS carbine. None of these are huge differences, but they add up I guess. I'm not an expert, but it is my take on it. |
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Might as well post mine,
BCM 1/8 18" ionbond BCM BCG Larue Gasblock KAC Freefloat KAC 600m rear KAC front 2 stage trigger A2 stock/flattop Topped with this in Larue http://swfa.com/Trijicon-3-9x40-Accu-Point-Rifle-Scope-P12874.aspx |
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When talking about the different gas systems on a 18" barrel, think about the distance from the gas hole to the end of the barrel. The longer that the bullet is in the barrel after the bullet passes the gas hole, the more gas that is getting pushed back through the gas tube. The end result is a sharper recoil impulse.
This is why on a 16" barrel, a mid-length gas system is slightly smoother than a carbine gas system. A mid-length gas system on a 18" barrel is much like a carbine gas system on a 16" barrel, the recoil impulse is going to be sharper due to the longer dwell time. The distance from the gas hole to the end of the A2 flash hider on a 18" barrel with mid-length gas system is approximatley 9.5". The distance from the gas hole to the end of the A2 flash hider on a 16" barrel with carbine-length gas system is approximatley 9.5". A intermediate gas system on a 18" barrel is simular to a mid-length gas system on a 16" barrel. The distance from the gas hole to the end of the A2 flash hider on a 18" barrel with intermediate-length gas system is approximatley 7.5". The distance from the gas hole to the end of the A2 flash hider on a 16" barrel with mid-length gas system is approximatley 7.5" The rifle length gas system on the 18" barrel will be the softest shooting of the 3 gas systems listed. You will find that most run and gun rifle competitors and 3 gunners prefer the rifle length gas system on 18" barrels because of it's softer recoil impulse which aids in faster follow up shots. 
03designgroup | Carbine vs. Mid-Length Gas System on a 16" Barrel 
Keep in mind that the -14.5" with carbine length gas system -16" with mid-length gas system -18" with intermediate gas system -20" with rifle length gas system have approximately the same dwell time (distance from the gas port to the end of the barrel). Click on this link: http://www.bushmaster.com/anatomy_bushmaster.asp - then click on "SPLIT" at the bottom of the screen. Then watch the cycle of operation. Note where the gas port (gas hole) is located. Watch as the bullet travels down the barrel and past the gas port. Think about the information I posted above. If the barrel were longer, it will result in more gas being pumped into the gas tube and into the action of the carbine. More gas equals more force, more force equals a higher recoil impulse. Kind of hard to explain on the internet, much easier to show someone face to face. Hope this makes sense. |
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This is all good info thanks. I did notice that Noveske and a couple other vendors are utilizing the mid length gas system, but a look at the MK 12 Mod 0 reveals a rifle length gas system. So that is why I was wondering what the preferred is now.
I do plan on using a supressor, and more than likely I will probably be going with a rifle length gas system. Thanks for all the gouge. S/F |
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Quoted:
This is all good info thanks. I did notice that Noveske and a couple other vendors are utilizing the mid length gas system, but a look at the MK 12 Mod 0 reveals a rifle length gas system. So that is why I was wondering what the preferred is now. I do plan on using a supressor, and more than likely I will probably be going with a rifle length gas system. Thanks for all the gouge. S/F Yea, if you are going to use a suppressor, then go rifle length on an 18" barrel. |
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