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Mid-Length vs. Rifle Length gas system questions.


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#1 sasquatch981

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Posted 03 November 2009 - 12:18 AM

So I am thinking of building a new upper for local Tac-Rifle Matches. I want a 18" barrel, but the (2) barrels I am looking at have different Gas systems. One has a mid-length, and the other has a rifle length. My first idea was a 16" rifle with a pig-tail to make it a rifle length system. Is there a "big" differnce between the 2 systems mid or rifle, or would I be better suited with one or the other. I am still trying to decide if I want to put it on my current carbine lower with Magpul CTR stock and Endine buffer, or a new lower with a Vltor rifle length mod-stock and rifle length Endine? Would the 2 different systems cause problems on the 2 different lowers. As for comps I was thinking of a Cooley Comp, or TTI Recoil Ellimantor. Do you think that would pose any issues with the gas system? Thanks.
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#2 blkbrd

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Posted 03 November 2009 - 12:59 AM

I love Endine buffers, they have allowed me to beat shooters that were better than me because there endine buffers failed <_<

Pigtails don't make carbine gas systems much softer at all. Rifle length gas systems are the way to go if you want a soft shooting rifle.

CTR stocks grace most of my rifles now, even my 20" ers.

For the ultimate shooting match rifle you want it matched with your buffer. I prefer the lightweight JP stainless carrier and a standard carbine buffer, with the gas turned down to function with Wolf ammo which gives me just the right gas cushion with my reloads.

Check the latest issue of front sight for a good article on comps.

#3 cking

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Posted 03 November 2009 - 01:14 AM

pig-tails don't fix the problem. Its the gas pressure at the port thats the problem. So I believe Armalite lays claim to promoting the mid-length which is about 2 inchs longer than the M4. The closer the port to chamber the greater the pressure, you get more port erosion per round at the closer port also. Also too close to the muzzle and the duration of gas pulse could be a problem. The AR has rather long leaky gas passage [sic...] compared to short stroke guns like AK or Garand. The 18" barrel with rifle length system without a muzzle brake may or may not cause problems.

So nature of problem is the M4 has a pretty violent extraction which migated by the rubber donut on the extractor. Plus a big problem with M4 is burning mag after mag in full auto gets it too hot especially the end of that gas tube. The more rounds you shoot the more gas port erodes and more gas, pressure goes up and so does the auto cyclical rate. Then more failures.

So for 18" barrel you can argue mid or rifle length, but skip the M4 length. I've built two 18"s' with mid-length and I'm using Douglas SS Blanks done by Compass Lake. One is a Stag based Lefty. Both work fine.

#4 00bullitt

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Posted 03 November 2009 - 07:33 AM

For competition based rifles....I prefer rifle length or intermediate(not mid) length gas systems on 17 or 18" barrels for the smoothest recoil impulse. I also prefer to run rifle length buffers and stocks. Preferrably the Magpul PRS.
and for comps....I choose the SJC Titan. And as for Enidines.....run one if you like but the fellow above hit the nail pretty squarely on the head.

Speed is Fine,Accuracy is final....but accurate hits at extremely high speed is final much faster.


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#5 dmshozer1

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Posted 03 November 2009 - 07:45 AM

Most of the guns used in 3gun lately are 18 inch, rifle length gas. Why? Because they are very soft shooting and reliable!
There is a lot of good information on this subject in recent posts.
Read them carefully. As usual, some is B.S. and some is very good.
Trust me, 18 inch, rifle gas=a nice system!

#6 StealthyBlagga

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Posted 03 November 2009 - 08:41 AM

You might also want to re-evaluate the benefit of 18" vs 20". The difference in length is very small (2", duh), and confounded by your choice of muzzle brake. The 20" route has a lot of upside: wider selection of barrels, more reliable with rifle length gas system, higher velocity, longer sight radius (irons). A lot of top 3-gunners run 20" guns just fine, and this is the route I would recommend if your local matches have targets out beyond 200yds. If your local matches are all at shorter range, and benefit from a shorter rifle, go to a 16" midlength.

#7 Mike Singer

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Posted 04 November 2009 - 08:12 AM

If you use an adjustable gas block does the length of the system really matter?

#8 blkbrd

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Posted 09 November 2009 - 04:03 AM

Yes it does. A long soft push is less violent, than a short hard push.

#9 Xfactor

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Posted 09 November 2009 - 08:06 AM

.. A long soft push is less violent, than a short hard push.

That's what she said!! :roflol:

Sorry... couldn't pass that one up!
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#10 Mike Singer

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Posted 18 November 2009 - 11:25 PM

So what is a descent 18" barrel? I don't want to pay a fortune for a designer barrel. If you have all the necessary parts and pieces can you just get a barrel and put the rifle length gas system on it? Does the barrel need to be set up for the gas system? Could I put a rifle length system on a 16" barrel?

#11 OPENB

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Posted 19 November 2009 - 06:33 AM

The barrel port location IS the gas system. A 16" carbine barrel will have the port hole closer to the chamber, requiring a short, carbine gas tube. Rifle length gas tubes are used on most 18-20" barrels, and mid length is in between, a compromise between carbine and rifle. I am using a WOA 18" SS barrel with rifle length gas system, 1/8 twist. I got it at Ranier Arms earlier this year for around $300. I had ordered a DPMS M12 18" barrel for around $180, but there was a YEAR long wait on it. If I was doing this all over again, I would get the DPMS 20" chrome moly barrel from Brownells for $140, shoot the hell out of it, and repeat as necessary (when it gets over 2MOA groups). I think it was Benny that said the DPMS barrels shoot so much better than what you pay for them. As to your last question, DPMS does make a 16" barrel with a rifle gas port location. I know Chris Keen has one, and it runs great for him. I have heard others say they don't, so you may want to look into that one further.

#12 Mike Singer

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Posted 19 November 2009 - 08:22 AM

Thanks for the info. I'm going to see if I can find an 18" DPMS barrel cut for a rifle length gas system.

#13 Mike Singer

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Posted 19 November 2009 - 07:25 PM

It looks like Brownells has a 20" DPMS barrel that will take a rifle length gas system. Wow do I go about having it cut down? Where do I look for someone to cut it?

#14 OPENB

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Posted 20 November 2009 - 08:15 AM

I've had several barrels cut and turned by ADCO in Toledo. Fast turn around, and great work. I will have him do my WOA this winter after Ft. Benning. If you get the 20", what are you getting it cut down to? If it is to 18", I'd suggest it might not be worth the expense for 2". If it is to 16", DPMS makes this barrel already, and you wouldn't have to get it cut. Plus, the gas port should already be correct size, and you wouldn't have to have it enlarged. Just some observations.

#15 Revopop

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Posted 21 November 2009 - 12:10 PM

DPMS calls it the "Tactical". 16" barrel, rifle length gas.
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#16 peabody

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Posted 13 August 2010 - 12:43 PM

i have a cmmg barrel, re-done by steve at ADCO. great work and fast.

its a mid-contour barrel [too heavy] , so steve trimmed her down, and moved gas port to a middy.


AWSOME.

having said that... i want a DPMS 16'' with rifle gas so bad , i can taste it.

already have a 20'' service rifle, its the cats meow, for accuracy and soft shooting.


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#17 512bpg

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Posted 08 February 2012 - 05:38 PM

just the topic ive been researching... I currently have a dpms lr 308 with the 24" bull barrel. It has worked flawlessly from day 1 so of course I want to mod it already :)

Wanting to cut the barrel down to 18" if possible (20 if its not a smart idea) and have been seeking out info on whether this will mess up the cycling since it has the rifle gas system on it and 18 would bring it down to just past the has block. I do plan to put a brake on it but want it to work without one for a while first. Can I just do a cut and crown on it or are the ports going to need to be resized for it to work properly? It currently has the A2 stock and buffer that came with it and i'd like to put the PRS on it eventually but cant think of any other mods i have in mind that would affect cycling.

Thanks in advance for any answers as I try to sort this out before getting the barrel hacked!

#18 Lead-Head

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Posted 08 February 2012 - 05:59 PM

20" GI profile barrel. A good one. Ususally cost around $240. chrome lined 4150 CMV. Chambered in 5.56. For me, is a hard barrel to beat. Not reaally a "competition barrel" but they have positive attributes. These are not Light enough to quickly drive the rifle from target to target .. Longer sight radius for irons. Rifle length gas or course. Easy to build a 1.5 moa rifle from and maybe better than 1.5 moa.....I don't own an AR with a scope so maybe they shoot better than the width of my front post.
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#19 shooter545

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Posted 09 February 2012 - 07:21 AM

I did the same thing to a DPMS LR-260; went from 24" to 20" same MagPul PRS with no issues. I have since gone to a 20" Bartlien barrel that is a lighter weight profile but the other barrel shot and ran just fine with no change to the gas port. YMMV.

#20 512bpg

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Posted 09 February 2012 - 08:40 AM

when considering length, would you take into account the muzzle brake? now deciding whether to cut a 24" bull barrel down to 18 or 20 since the brake is going to add another couple inches




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