kwrangln Posted September 3, 2009 Share Posted September 3, 2009 Bear with me here as I try to get into a little background for my question. Lots of talk in the 3 gun community about how much smoother middy or rifle length gas systems are than carbine length gas systems, longer the gas system the easier the action is as it pushes the bolt carrier group to the rear during cycling. Most folks here will agree that a carbine length gas system is a more violent cycle than a middy or rifle length system. With all that being said, what's to stop us from using a longer gas system on barrels drilled for carbine length systems? I'm not talking about plugging the current gas port and redrilling further down the barrel, I'm talking about just using a longer gas tube. Nothing says the gas tube has to be straight does it? Basic hydrolics says pressure is exerted equally in all directions, so straight, curved, etc doesn't matter. Thinking outside the box, the gas tube could make a spiral around the barrele, or simply curve side to side to add length allowing more space for the gas to expand softening the action as it does so. I've seen mention on the board here gas tubes called "pig tails", and "big tubes", but no further info yet, anyone know anything about them? Anyone tried using a longer than stock gas tube on their AR? What were the affects? Just thinking things through some playing around with buffer weights would be required to balance things out with the now longer gas system for reliability, but is the experiment worth it? From what I'm reading in the 3 gun world, a rifle or middy length gas system and a good comp would add greatly to keeping things nice and flat making for faster follow up shots. It'll also be a lot cheaper to play with gas tube lengths than it would be to replace a barrel, so why not. One point to consider that I don't have dimensions for is length of gas pulse with the different barrels, the distance between the gas port and the end of the barrel, to compare. Since gas is only under pressure to the gas system from the time the bullet passes the gas port until it leaves the barrel, the distance between the two should play into the effectiveness of the gas system reguardless of length, but can be worked around with varying gas port sizes. Anyone care to post up some measurements on different setups for the distance between the gas port and end of barrel? Being a tinkerer can be fun, and rewarding if it works, so why not? Not like I'll be making any permanent changes to the rifle or barrel, so if it doesn't work, just throw the stock gas tube and buffer back in and carry on. Any info or links yall can find to help out will be appreciated, thanks. Link to comment Share on other sites More sharing options...
n2ipsc Posted September 3, 2009 Share Posted September 3, 2009 You mean like THESE? I have one of these on a 16" "tactical" AR, with an Enidine AR-Restor and a JP Cooley/tactical comp, and it's very, very flat shooting; seems to be a good combination. Link to comment Share on other sites More sharing options...
Pat Miles Posted September 3, 2009 Share Posted September 3, 2009 Brownells sells pigtail gas tubes for carbine length (10"-16") barrels to address this problem. They are a bit pricey though. ADios, Pat Link to comment Share on other sites More sharing options...
kwrangln Posted September 3, 2009 Author Share Posted September 3, 2009 Outstanding, thanks guys. I didn't even think to check Brownell's, they are proud of them things aren't they, $86 for a gas tube? N2ipsc, did you do all those mods at once? How much tuning did it take after swapping to the longer gas tube to make it function reliably? Just thinking here, but the carbine buffer is heavier and has a stiffer spring to account for the harshness of the cycling, so a softer cycle would short stroke correct? If I'm on the wrong track, please let me know. Thanks again guys, now I don't feel like it's that crazy of an idea. Link to comment Share on other sites More sharing options...
XRe Posted September 3, 2009 Share Posted September 3, 2009 Carbine buffer is lighter than a standard AR buffer... Only an H3 weight carbine buffer is heavier... http://m4carbine.net/showthread.php?t=6827 Link to comment Share on other sites More sharing options...
kwrangln Posted September 3, 2009 Author Share Posted September 3, 2009 Carbine buffer is lighter than a standard AR buffer... Only an H3 weight carbine buffer is heavier... http://m4carbine.net/showthread.php?t=6827 Thanks for keeping me straight XRe. I'm going to have to wrap my nugget around force vs reciprocating weight for a bit. Link to comment Share on other sites More sharing options...
jnikoley Posted September 7, 2009 Share Posted September 7, 2009 If you want to adjust the amount of gas, why not go with an adjustable gas block like the PRI, Firebird, or JP? Link to comment Share on other sites More sharing options...
wsimpso1 Posted September 8, 2009 Share Posted September 8, 2009 Pigtails are pricey, as are fat gas tubes, but if they smooth out your gun and make it reliable, well, it will hold you until your new 16" with a midlength or 18-20" with a rifle length gas system arrives. The big problem with shorty gas systems in 16" barrels is the timing of the operating pulse. Adjustable ports may help a little, but the gun may still be picky about ammo, how you hold it, etc. Derrick Martin wrote a whole chapter on the topic of making unreliable 16" shorties work NINE YEARS AGO. Every case rim ripping AR15 I see is a shorty. Why do folks keep buying them? Billski Link to comment Share on other sites More sharing options...
sasquatch981 Posted September 14, 2009 Share Posted September 14, 2009 I have shot N2IPSC's rifle at local matches before. I have to say that shooting his rifle is like cheating! It is the flatest, and softest shooting rifle I have shot. I have talked to Floyd extensively about the rifle, and I am in the process of compiling the parts as we speak. I will say that he does not have a carbine buffer tube on the rifle, but rifle length stock. Link to comment Share on other sites More sharing options...
jobob Posted September 14, 2009 Share Posted September 14, 2009 I'm not sure I buy all the talk about carbines being unreliable. I have one 20" and 3 carbines, and the carbines are less ammo-picky than the rifle, by far! They aren't as soft or flat shooting, but, in my admittedly limited experience, are more reliable. The only AR I have (or had, as I recently sold it, like an idiot) that has never had a malfunction of any kind is a DPMS 16". Link to comment Share on other sites More sharing options...
wsimpso1 Posted September 14, 2009 Share Posted September 14, 2009 Don't get me wrong. I have seen rifle length guns that were screwing up - gunsmithing problems, gas rings missing, McFarlane rings, extractor worn out, cracked feed lips on the mags, etc. And more than few shorties work great. If you have 16" that work, hang onto them. But statistically speaking... The only time I have seen rifle length guns rip through the rim is when the chamber was just loaded with grit and/or goo. I have worked with several 16" shorties that rip through case rims even when clean, with polished chambers and new extractors, etc. And I have worked with a couple guys whose 16" guns we never did get running reliably. The gas pulse comes too big and too early. Some folks bump the gas port size, which just makes it worse. With the pretty good chance that a new 16" shorty will act up and require special attention, why bother with them? Add either a Fat Tube or a Pigtail to fix them until you can rebuild it with a new barrel in either mid length or rifle length gas system. Billski Link to comment Share on other sites More sharing options...
StealthyBlagga Posted September 14, 2009 Share Posted September 14, 2009 The fat or pigtail gas tubes may have some marginal benefit, but the real root cause of carbine functional problems is not the length of the gas tube, but the location of the gas port and the gas pressure at that location. The chart below speaks for itself: As a short-term fix, you could try the MGI adjustable gas tube (a drop-in part), but the better solution - and probably cheaper in the long run - would be to sell your current barrel (or upper) and replace it with a midlength (16-18") or rifle (18-20") barrel (or upper). Link to comment Share on other sites More sharing options...
jobob Posted September 14, 2009 Share Posted September 14, 2009 (edited) Are Mcfarland rings a problem? Also, ripping through the rim is not the only function problem, nor most common problem, associated with ARs. I've seen it happen a couple of times, mostly in relation to Wolf ammo, or first brass cased round fired after shooting Wolf steel cased ammo. Yes it happened with carbines, but I also had one in an 18" rifle length piston system. Most of our troops are armed with 14.5" carbines with carbine gas systems, and for the most part they seem to function fine. Perhaps the carbines have a shorter life span due to the extra battering in the higher pressure gas system, but the platform is compact and very useful in the type of combat they are in. I had a 16" Colt ride with me for 15 years in my patrol vehicle, and that was much preferable to packing a rifle. Also, that carbine never, ever malfunctioned, and I'm not a Colt fan. So, there are many reasons, really, for choosing a carbine over a rifle, and most are related to convenience. I suppose a mid length gas system would be a little preferrable, but until they are as commonly available as carbines they won't replace them, and for me the carbines work just fine in the meantime. Edited September 14, 2009 by jobob Link to comment Share on other sites More sharing options...
wsimpso1 Posted September 16, 2009 Share Posted September 16, 2009 The shorty gas system was designed for 11" machineguns and 12-14" carbines, and they seem to work fine. In a 16" barrelled shorty, we get higher pressure gas, we get it too soon, and we get it for longer. Now some 16" guns work fine, but some just refuse to become reliable... Build a 16" gun with the port in the right place (mid length upper) or a 18-20" upper with a rifle length system, and they just work. And people that build HighPower Match Rifles on the AR platform they use still longer barrels, and find that they work better with the port moved further out still. It seems like four inches is all the further the port should be from the muzzle. Yes, MacFarland rings can be the problem. I watched a Master Class shooter with a Scott Medesha space gun (Gold standard for NRA Match Rifles). Spaces guns usually use carbine buffers... It would start a string OK, but the empties would come out more and more forward until the gun would not even eject them. After much fuss with cleaning and lubricating, installing a new gas tube, the MacFarlane gas ring on the bolt was replaced with three GI rings, and the gun was back to its x-ring drilling form. Billski Link to comment Share on other sites More sharing options...
jobob Posted September 17, 2009 Share Posted September 17, 2009 (edited) That's interesting. I've put the McFarland rings on a couple ARs with no problem, and a problem with one. What is it about the Mcfarland ring that could be causing the problem? They do seem to fit slightly tighter than the 3 standard rings, so if it's in a slightly undersized carrier it could cause a problem. That did happen with my 20". I tried the McFarland because the gun is pretty ammo sensitive and thought it would make it more reliable. The effect was just the opposite. After a few shots, no matter how much lube I stared with, there was so much drag between the bolt and carrier that it would not function with anything but full power mil spec ammo. A squirt of oil would make it work for a few rounds, then start short stroking again. Went back to the 3 rings in that rifle and it got better, though it's still ammo sensitive (won't function with Wolf). Speaking of throwing the empties forward, I have a POF upper that throws them at around 12:30 to 1:30. I've been waiting for it to start malfunctioning, but it just keeps shooting with monotonous reliability. Always wondered what causes it, but it certainly isn't too tight gas rings, since there aren't any! But it works, so I don't think I should try to fix it. Back to the original topic. I was looking at those pigtails at Brownell's and decided to do a little searching before getting one of those overpriced tubes. Best I can find out is that they may cause malfunctions. Bottom line, if your gun is working, don't change it. If it isn't working, it's something to try. Edited September 17, 2009 by jobob Link to comment Share on other sites More sharing options...
StealthyBlagga Posted September 17, 2009 Share Posted September 17, 2009 (edited) Speaking of throwing the empties forward, I have a POF upper that throws them at around 12:30 to 1:30. I've been waiting for it to start malfunctioning, but it just keeps shooting with monotonous reliability. Always wondered what causes it, but it certainly isn't too tight gas rings, since there aren't any! But it works, so I don't think I should try to fix it. In my experience, forward ejection on a standard DI AR15 is an indication of excessive bolt velocity. Going to a heavier buffer or throttling down the gas will bring the ejection pattern back towards 3 o'clock (which is where I like it to be). I can't comment on whether this is what you are seeing on your POF piston upper, nor if it is even a problem on that platform. When we talk about DI guns, however, unfortunately the port pressure in the carbine gas system is so high that gas port erosion can accelerate and bolt velocity increase over a comparatively short timeframe (maybe only a few thousand rounds)... this can mean a carbine that runs great when it is new can start to malfunction within a matter of months of our kind of shooting. In general, if someone asks my opinion, I will ALWAYS advise them against a carbine gas system in any 16"+ barrel. For our sport, midlength is the minimum people should be considering IMHO. Edited September 17, 2009 by StealthyBlagga Link to comment Share on other sites More sharing options...
EkuJustice Posted September 18, 2009 Share Posted September 18, 2009 Never had a bit of trouble from my 16 inch guns with the carbine gas system. Havent had any trouble with the shorty either that is a 10.5 inch. The 10.5 should be even more unreliable but has never choked once Link to comment Share on other sites More sharing options...
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