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Gas System for .308 AR-Carbine or Middie?


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i have a DPMS Oracle with a carbine length gas system.  is there any reason i should go to a mid-length system for my .308?  it seems to run just fine as is, but i keep reading about mid-length systems being preferable for one reason or another.  is this just internet hype or is one better than the other for our big AR rifles?

liontribe

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I say, you wouldn't have bought an AR if you don't plan on changing it at some point.

I think you should go to a rifle length. The 308 is over gassed as it is. I know 1 or 2 guys here have 16" barrels with rifle length gas. I just ordered a 17" with rifle length gas.

If you're looking to conceal the gas block, the mid length is as short as I would recommend.

I wouldn't go to a carbine unless barrel length gave me no other option. I just switched my last AR15 over to a 14.5" mid. I'm done with carbines, at least till I can finagle a SBR.

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Ill vote for if it aint broke dont fix it.

+1 , don't feel like you have to change it, it's all personal preference unless it's giving you fits. if you decide to change, do all your research first, bounce questions off us, we'll help.

mostly though i feel if you are enjoy shooting as is leave it. it's too easy to get caught up in the kool aid.

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I think that the carbine length gas system being a bad thing originated with the M4's. I have read that they were very hard on bolts because of the earlier gas pressure on the carrier effected the timing and this caused the bolt to be trying to cycle and extract the case too early, before the case pressure had diminished sufficiently. I have a mid length gas system on my 14.5" 5.56 gun and prefer it to the carbine setup. I find that the gun seems to cycle smoother and recoil is less. Now if you were to apply the same logic to the .308, I would think that the mid length gas system (or rifle length for that matter) has the potential to give you a smoother operating gun. Of course the 7.62 is not the same rd as th 5.56 so the gas impulse will not be the same.

Personally I have a 14.5" 7.62 AR with what Noveske calls a carbine gas system, But the GB is actually located in the same place that an AR 15 mid length gas block is located. I wouldn't want the gas system on my 14.5 gun to be any longer than it is for reliability reasons. That being said, a 14.5 barrel is a different animal than a 16". Barrels are expensive, If your gun runs well as is, I'd be inclined to leave the system alone. You could put a heavier buffer in it. The only reason I'd consider a different gas system type would be if you wanted to change the barrel, not to change the barrel because you want a different gas system.

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That being said, a 14.5 barrel is a different animal than a 16". Barrels are expensive, If your gun runs well as is, I'd be inclined to leave the system alone. You could put a heavier buffer in it. The only reason I'd consider a different gas system type would be if you wanted to change the barrel, not to change the barrel because you want a different gas system. want the gas system on my 14.5 gun to be any longer than it is for reliability reasons.

well said

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thanks for all the quick replies.  i have installed the buffer set-up from slash.  i am also thinking of going with an adjustable gas block in the near future, just in case i run into a problem with certain loads.  it is my main hunting rifle and i have only had one FTE with a round that it had no troubles with before hand.  i have a bit of tax cash coming my way.  i have been debating another rifle or just working this one over exactly as i desire.  tough call.  i have only put maybe 150 rounds through this gun with the one failure to cycle.  it isn't even broke in good yet.  i feel the need to customize everything though.  i am a knife maker and i can't leave anything as is.  :cookoo:

liontribe

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Ill vote for if it aint broke dont fix it.

Such wisdom , it gets my vote also.

I have one question , why a adj. gas block for a hunting rifle ?

The only thing it would do is restrict gas flow, not some thing you want with a hunting rifle . If your rifle doesn't function correctly with a certain type /manufacturer ammo , I would stay away from it .

Your gas system is wide open now , restricting it may cause problems .

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from what i have read and my experiences with AR rifles, the big .308s are many times over gassed.  with an adjustable gas block i can fine tune for a wider variety of loads.  some commercial loads are on the hot end of the spectrum and could possibly cause problems in an autoloader.  adjustable gas block would just give a wider range of choices.  i like plenty of choices.  and that is one of the fun things about AR rifles, they are like legos.  i liked legos.  <thumbsup> 

liontribe

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I like to refer to my conversations with John Paul of JP. According to JP much of the 308 ammo was designed for bolt action rifles with no regard to semi auto funtion, reliabilty and wear. Often the pressure curve of ammo is not ideal for the semi auto and in fact most rounds do over gas the weapon. These semi's were originally designed to fire very specific military rounds.

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that block in your link looks like just the thing.  that was my thinking as well on many of the commercial .308 loads.  they vary greatly in pressure because that is of little worry to most modern bolt guns.  i like the idea of tuning my action for my pet loads or favorite commercial fodder.  i used to be a big FAL shooter and that is a great thing about those rifles.  fully adjustable gas system.  thanks for that link.  i will be doing some not so scientific experimenting with this rifle over the summer.  i will keep everybody up to date on my tinkering results.  i am very pleased with this rifle as is, i just want to see how versatile i can make it.  thanks for all the input.

liontribe

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  • 1 month later...
  • 3 years later...

Im building an LR 308 and have almost finished it up , Just got the BCG yesterday from WC Armory ... a complete NIB DPMS Platform BCG for under 150 .00 shipped ... Its frikin sick beautiful to say the least made by Tool craft its the best deal Ive found in a while  ...

 Enough on that part .... I couldn't wait to stick the bcg in and cycle it a few times , When I put it in the upper it was great ....once I started to cycle it a few times ...the buffer /spring compressed and stayed compressed until I knocked it loose from behind , had to remove the stock to punch it out .... Im running a regular length AR 15  buffer tube and  it seems to barley be long enough .... Im running a DPMS , LR 308 spring and 2.5" buffer so that stuff is correct , my tube is 7"3/4 .... The BCG is 8"3/4 so how is this gonna work ?

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 You could have started a new thread on this if you wanted too , this one is a little old , but resurrecting old threads don't bother me at all .

 

  What stock system are you running , a Carbine or Rifle stock ?

 If your Buffer is sticking in the Receiver Extension ( Buffer tube ) it may just as simple as needing more Lubricant . 

 Is your 7 3/4" measurement on the inside of the  Receiver Extension or outside measurement ?

 Your Buffer is the length for a DPMS type 308AR carbine , how long is your spring & how many coils in it ?

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