Barms

length of gas systems..

10 posts in this topic

Yes i try to do research before asking questions..

 

http://www.03designgroup.com/technotes/carbine-vs-mid-length-gas-system

 

but you guys just give the best info and advice..

 

so on a 16" barrel what is the main reason you chose your gas system length? It is performance? wear/tear? the front sight distance?

 

thanks..

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I went with a Spike's 14.5 Midlength upper and put on an A1 fixed stock since adjustable ones don't adjust in the People's Republic of NJ. I had hoped to be able to use a rifle buffer for it but found it to be undergassed. I ended up having to use a spike's spacer and an H buffer. The gun cycles very reliably now. I used to get the occasional FTE with the rifle buffer and spring. And man was it a **** to get unstuck..

My Colt 6940 (16" barrel, carbine gas system) has some stout ejection. Maybe that is why it doesn't like steel cased ammo and the Spikes is OK.

I have read that article before and think it is pretty dead on.Next time around I would swap and get the 14.5 in carbine and 16" in mid-length and save having to tinker with different buffers.

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so in laymans terms.. the longer the distance between the gas break and the muzzle (or i.e. a SHORTER system) gives more kick.

 

okay i'm clear on that.. but what are guys other preferences between the two? Is there some sort of tactical reason? or is it just a comfort preference on reliability and functionality?

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I'm no pro, but this is what I learned from my research on the topic a long while ago. I'm sure I'm leaving some stuff out....

 

Mid or rifle length are the ways to go. I don't know of any advantages with carbine length unless its necessary when building a SBR.

 

I own 14.5", 16", and 18" barrel length AR's all with mid length gas systems, and I couldn't be happier. All use the standard carbine buffer. I shoot everything from silver bear 62's, surplus 55's, and hand load 69's.

 

Its all about the tune state of the rifle. The balance of gas being sent back to the BCG, and the force it needs to move the buffer and spring back. Too much gas and/or not enough buffer weight to compensate equals a harsh recoil of the BCG (beats the gun and you up for no good reason). Too little gas and/or to heavy of a buffer weight will result in short stroking and jams, the BCG won't be sent all the way home for the full ejection/reload cycle.

 

Length of barrel, length of gas system, weight of buffer, and type of ammo (especially bullet weight) all come into play when it comes to how an AR's gas system in general will operate. You would want a setup in which ample gas is sent back to keep the rifle reliable, yet not overdone to the point that so much gas is being sent back that its just needlessly beating you and the gun up. From a performance perspective, over-gassed AR's I would think would have a disadvantage during quick follow up shots.

 

For the most part, any quality pre-built AR upper that you would purchase would already be good-to-go with any commercially available or surplus 5.56 ammo we can get. Building the upper from scratch, there is a chance that some tuning may need to take place , for instance with the gas port on the barrel and/or using an adjustable gas block.

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Like the others before me, I too would prefer a mid-length. Mechanically speaking, raz-0 covers it. And the others covered the preferential aspect (felt recoil). The extended sight radius is a plus if one were to run irons. And more interesting, IMO, are the Dissipator systems. The current generation are mostly mid-length systems with a full rifle-length sight radius. Dissy's aren't for everyone, but I really dig'em

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its dependent on the barrel length, too. Just for a hypothetical, if you have a carbine gas system on a 14.5" it would kick more then a mid length, however an 18" barrel with a carbine gas system will kick more then 14.5" since there is more pressure asserted for a longer period of time. moving the gas port down the barrel as the barrel gets longer ensures you get enough gas to cycle but not so much that it is essentially wasted, prone to malfunction, and more violent.

 

Technically you can tune the rifle from either end, the gas port location(how much gas is sent through the system) or at the buffer. However, adjusting the gas port location is more beneficial. Limiting the gas is better then compensating for it, you get a more efficient rifle with less kick, and for all purpose your internals see a lot less stress. The carbine system is technically for short barrels, i'm not sure why they put them on 16" barrels other then a popularity thing with "looks". Personally i don't even see the need for it on a 14.5" My BCM 14.5" is mid and it replaced a 16" mid with no other mods and works flawless.

 

18" seems to be the compromise for mid/rifle gas systems, and companies like Noveske came up with the "intermediate" gas systems, because they found the rifle cycles the best is that config, the compromise between recoil, cycle time and reliability. with a rifle length you would use a lighter buffer and for a mid a heavier one. So switching to intermediate gave less recoil then mid, and cycled better then the rifle length. But we start to loose standards here which is important in the AR world. If another company makes an Intermediate... is it the same as Noveske? They even include the tube and gas block with the barrel( and rightfully so at that price!) Do i have to by my gas tubes from noveske? or take the task to make my own?

 

there are gas blocks with adjustable pressure options, not sure how they fair though.

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Since there are already plenty of tech reasons given I will not go into that. IMHO, another reason to go with the mid is it just looks better than a carbine. I cant stand the look of a 16" carbine length, too much barrel sticking out in front of the FSB, especially when compared to a 14.5" midlength which looks perfect, again this is just my .02

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