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Gas system ???


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So I'm looking for some general info on the gas syste, Lots of variations out there. I have a rifle length system with a non adjustable block. I just went with the standard with what I was doing which is long range.


1.) It seems most say the .308 is over gassed. Does turning it down lessen recoil? I don't know how good or bad mine it... usually start feeling it after about 100 rounds.


2.) I'm considering building a light weight carbine length upper... no time soon. But I do not understand the trade offs with different length gas systems and different length barrels. I only want a carbine length for wieght and mass for a short CQC set up without being real concerned with distance.

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you can get a 17" barrel with rifle length gas if its important to you. From what I can tell, the main difference is without an adjustable gas block to control it, having the longer expansion length of a rifle gas system smooths out the motion, which will result in less felt recoil.

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Fulton Armory makes a 16" rifle length barrel..... So sexy!

If you like the idea of an adjustable gas block, you need to look into the JP (LMOS) Low Mass Operating System. The idea is to use the minimum amount of gas to cycle the rifle. The lower the weight of the cyclic mass, the less amount of felt function of the rifle.

They say that the felt recoil is actually 3 parts all felt in conjunction. First you feel the recoil of the shot. Next you feel the action pulling back and releasing the spent casing. The last you feel the bolt slamming back into battery.

JP designed the tank brake, the LMOS BCG, the adjustable GB and the captured buffer spring, all to address these issues. They sound great in concept. Since they were made by JP I assume they work and are very high quality. The problem is reliability. Even JP advises against using the parts in a hunting/combat rifle, where every pull of the trigger counts.

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So, sort of forgot. Thanks guys

For a carbine length system, what are the drawbacks? I would assume you would need an adjustable block at that point to turn it down a bit. My thinking is just to have less "retational mass". You know, CCQ. Bring it around easier. Just guessing really. I also saw that less weight up front hurts follow up... in genral. just thought. If it is no big deal, then no reason to go out of my way... but a carbine length hand guard most certainly weighs less than a rifle length one. Trying to make it light.

Edited by Powerman
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Having a longer hand guard has its advantages,more room for your hand , of course , if using a bipod ,lets you mount it farther out towards the end of the barrel. The problem is , if you use a adj. gas block , you may need to make some way to adj. it ,through the hand guard.


I have two rifle length 308's ,a 16" & a 20" & am building a 18.5" & its a rifle length gas system. The 16",rifle length barrel , shoots fine . I would not have a carbine gas system in 308, but others seem to have them & they work fine .


The 308/7.62x51 has a lot of gas power when fired , The lighter you make them the more they will feel like they are over gased, that's for sure.

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I went with a 18" bull barrel (mid gas port) The adjustable block is nice, fully open and I was ejecting brass 4 stalls over. Keep in mind that as you break it in, you will need to re-adjust it. And when you change from lets say 147 to 180 grn you will need to adjust again.

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I would try to adjust it down to the widest range, even if it is a little over gassed for some.


The only reason I am considering this is to build a light weight carbine upper to swap out. I have a 20" bull barrel now with rifle length system, bipod and scope. I was thinking of a light weight 16" barrel with a carbine length gas system just from a short light stand point. Throw on some BIUS and a red dot and use it for fun stuff instead of long range.

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