6132expert Posted August 16, 2011 Report Share Posted August 16, 2011 OK, here is a good one I think.I know the different gas system lenghts in the barrels. I know they come in different variations with different barrel lengths. I primarily want to talk 16 inch and 18 inch barrels. Is there an ideal gas system lenght for these 2 lenghts? Which one would it be? I would imagine this ideal system would be very efficiant and have the ability to run the fire arm with no issue when firing any decent loads.The reason for this thought is the ER Shaw barrel I am wanting to put on my DPMS. I plan to call them tomarrow and just have a chat. There motto is whatever you want in a barrel they can do. I want a barrel that will run any ammo or about any ammo with no issues. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 16, 2011 Report Share Posted August 16, 2011 Rifle length gas, for both those barrel lengths. <thumbsup> Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 16, 2011 Author Report Share Posted August 16, 2011 Thanks for the input 98, but why? This is something I just cant grasp the concept of. Can you or someone help me understand why Rifle Lenght would be better then carbine or mid lenght. Is it because the gas tube is longer and can provide more energy to the gas key to drive the BCG back? Or what? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 16, 2011 Report Share Posted August 16, 2011 Thanks for the input 98, but why? This is something I just cant grasp the concept of. Can you or someone help me understand why Rifle Lenght would be better then carbine or mid lenght. Is it because the gas tube is longer and can provide more energy to the gas key to drive the BCG back? Or what?Timing, brother, timing. It's all about the location of the gas port that's drilled in the barrel, and how much barrel remains after that gas port (drilled hole). Until that bullet leaves the end of the barrel, it's holding in the gasses that cycle the weapon. The important thing is the location of the gas port and barrel length remaining after it (dwell time).Example - if you had an 18" barrel and a pistol-length gas system, that gun would kick the hell out of you. That same barrel with a carbine gas system is going to kick less than the pistol gas setup, but it's still going to beat the hell out of you (and the gun). Same barrel with rifle gas - that's going to be the softest recoiling of all the available combinations. Gas port SIZE makes all the difference in the world here - how much gas can pass through that hole - but most of these are pretty much set for the length of the gas system.Lots of people used to say you couldn't have a 16" barrel with rifle gas - and Fulton Armory made one. The nay-sayers thought it didn't have enough distance between the gas port and end of the barrel - not enough dwell time to cycle the weapon. Wrong - and it works really, really well. survivalshop (member here) has one. He'll probably be in here with more info. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 16, 2011 Report Share Posted August 16, 2011 There's more to it than just felt recoil, but that's the one thing that people can feel in the comparisons of different gas systems. Too much gas, not a tuned system - it beats up internal parts during recoil (lugs on the bolt, the BCG, the action spring and buffer, the barrel extension). If you're running an incompatible setup, you'll have the bolt unlocking too soon (the 18" barrel and pistol gas scenario from above, probably), not extracting properly. Not only does that affect extraction, but it affect accuracy, too.There's alot to it, but the best way to typically explain it is with the recoil examples... Quote Link to comment Share on other sites More sharing options...
Jgun Posted August 16, 2011 Report Share Posted August 16, 2011 I think i read somewhere that many of the problems associated with the M4 carbine are attributed to the carbine length gas system. I don't own a 16" AR with rifle length gas system, so can't comment on them from personal experience, but I definitely prefer the midlength gas system to the carbine gas system on a 14.5" or 16" 5.56 gun. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 16, 2011 Report Share Posted August 16, 2011 I was getting into this in another discussion, but here's some info on the gas systems and development:Gas systems have specific lengths to them, which are pretty much standard, unless you're talking about Armalite gas systems. I'll stay out of that for now.Carbine length gas system: 7.5" gas tube, designed around the mil issue 14.5" barreled M4 carbine.Rifle length gas system: usually around 13" gas tube, designed for the mil issue 20" barreled M16.Mid-length gas system: approx 9.5" gas tube, designed primarily for the civilian-legal 16" AR-15 "carbine."Notice similarities up there? I'll discuss further in a few.^^^ That was from a "rifles and carbines" thread here. Now, knowing dwell time now, as the distance between the gas port and the barrel end - time is takes a projectile to cover that amount of distance, actually.Distance to cover on the dwell time in the 20" M16A2 would be around 7", right? This is one of the factors that led to the AR carbine gas system. Barrel length for the shorter rifle being 14.5", and the gas tube ends up being around 7.5" - that's 7" of barrel, just like the A2 original config. The A2 recoil is more manageable, but it's also more gun. They feel similar. 16" being the civilian legal barrel length, when you combine that with a 7.5" gas tube/system - the carbine system - it's a harsher recoil. That's primarily where the midlength gas system cam into play. Middy gas on a 14.5" is a very nice shooting system. .308 ARs are different, though. What it takes to cycle an AR-15 doesn't carry straight over to a .308 Win cartridge. There's so much power and pressure in a .308 Win cartridge that it will cycle just about any ammo through a 16" barrel while using a rifle gas system. <thumbsup> Quote Link to comment Share on other sites More sharing options...
Robocop1051 Posted August 16, 2011 Report Share Posted August 16, 2011 There's so much power and pressure in a .308 Win cartridge that it will cycle just about any ammo through a 16" barrel while using a rifle gas system. <thumbsup> I had a talk with Mike Degerness at "Jense Precision" (also known as XPA). He advised that going to a 17" barrel would alleviate the issue of just about any ammo . I guess he had some issues with the lighter weight stuff??? Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 17, 2011 Author Report Share Posted August 17, 2011 OK, guys I have looked everywhere I know to look and I can not find a 16 or 18 inch rifle lenght barrel for my 308. Where are they at? <dontknow> Quote Link to comment Share on other sites More sharing options...
fr3db3ar Posted August 17, 2011 Report Share Posted August 17, 2011 Is it possible to nick a short port and have a longer one added? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 17, 2011 Report Share Posted August 17, 2011 OK, guys I have looked everywhere I know to look and I can not find a 16 or 18 inch rifle lenght barrel for my 308. Where are they at? <dontknow>Check out Fulton Armory, and see what theyve got available right now - I know they're making a bunch more barrel profiles now, than they had available in the past. Great stuff, too.Is it possible to nick a short port and have a longer one added?ADCO could tackle something like that, but I wouldn't have too many more places do it. Reprofiling the barrel for a gas block in the new position would be a PITA... Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 17, 2011 Author Report Share Posted August 17, 2011 I may call Fulton and ask, but they dont have one on the site. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 18, 2011 Report Share Posted August 18, 2011 http://www.fulton-armory.com/barrelfatitan16nmmedss1x10936gasblock.aspxhttp://www.fulton-armory.com/barrelfatitan185lwcm1x10750gasblockchrome-lined.aspxhttp://www.fulton-armory.com/barrelfatitan185nmmedss1x10936gasblock.aspxsurvivalshop owns the first one, and I own the 3rd one. Fire off questions about them, and we'll get the answers you need from an owner's perspective. <thumbsup> Quote Link to comment Share on other sites More sharing options...
fr3db3ar Posted August 18, 2011 Report Share Posted August 18, 2011 so, in lieu of what I've been reading here. An adjustable gas block can help take some of the punishment away from parts and body? Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 18, 2011 Author Report Share Posted August 18, 2011 Well dam how the hck did I miss those. Thanks for posting now I feel like a dumb ass........... <laughs> so is there going to be any benifits on the different gas block sizes? Also I hate there disclamer about there chambering may not head space to your bolt. Is it best to buy there bolt? Have you guys had any trouble firing any factory ammo at all? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 18, 2011 Report Share Posted August 18, 2011 No issues with any factory ammo, and I've shot 13 different brands of match ammo through it. I did use a Fulton complete BCG, though. Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 18, 2011 Author Report Share Posted August 18, 2011 If I was to order a Fulton barrel and crome BCG would they ensure that the head spaceing was correct? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 18, 2011 Report Share Posted August 18, 2011 Yep, when you order them together, they check it before it gets packaged for shipment. <thumbsup> Quote Link to comment Share on other sites More sharing options...
6132expert Posted August 18, 2011 Author Report Share Posted August 18, 2011 Great , that solves problem number one. Looks like Fulton will finish off my 308 here real soon. <thumbsup> Quote Link to comment Share on other sites More sharing options...
MR308 Posted January 6, 2021 Report Share Posted January 6, 2021 Well, I hate to be the guy that digs up old posts like this, but I’ve got a new kind of conundrum. So I’m building a 14.5” .308 AR10. I’m having mcGowens make a barrel for it but I’m trying to find the best set up. The barrel will be pinned and welded with a Gamma VG6 and I have been planning on using a mid length gas system. I’ve heard back and forth opinions about twist rate and I was initially set on a 1:9 for added flight stability but I have people tell me that may be “too fast”. The other thing I’ve been trying to figure out is if I can cram a rifle length gas system on a 14.5 inch barrel. Based on what I’m reading here that’s a no due to not enough dwell time, but I wanted to figure out if I could. I don’t know the numbers to crunch but I was looking for someone who did. My main thought process for this was that in a 14.5 the bullet would leave the barrel before all the powder in the casing has burned (at least that’s what I’ve read). So I assume that having a longer gas system would allow more pressure for a longer duration behind the bullet, this increasing muzzle velocity. Of course I don’t know a lot about ballistics as this is the first AR I’ve built and I’ve never reloaded, so this is all theoretical for me. Thanks for the help in advance! Quote Link to comment Share on other sites More sharing options...
unforgiven Posted January 6, 2021 Report Share Posted January 6, 2021 .308 is 1:10. Mid gas barrel is not long enough. Just my 2 mag's Quote Link to comment Share on other sites More sharing options...
unforgiven Posted January 6, 2021 Report Share Posted January 6, 2021 (edited) I have a M5 Aero w/ 14.5 barrel mid gas and Battle Comp compensator fixed. Edited January 6, 2021 by unforgiven Quote Link to comment Share on other sites More sharing options...
MR308 Posted January 6, 2021 Report Share Posted January 6, 2021 1 minute ago, unforgiven said: I have a M5 Aero w/ 14.5 barrel mid gas and Battle Comp compensator fixed. What do you mean by “not long enough”? As in go rifle length gas system? And it is commonly 1:10 in most barrels, yes. Originally it was 1:11.25, and I was asking 1:9 for bullet stability reasons out of the shorter barrel how are your groupings at 14.5” with a 1:10? - And how are they at range? Quote Link to comment Share on other sites More sharing options...
unforgiven Posted January 6, 2021 Report Share Posted January 6, 2021 Runs fine minute of man all day long. Comp works for follow up shots but comes with an extra cup of loud. I have Armalite recoil system in all large frame ARs. Aero M5 upper/ lower. Quote Link to comment Share on other sites More sharing options...
unforgiven Posted January 6, 2021 Report Share Posted January 6, 2021 I have only seen 1:9 for small frame ARs. Show my a .308 barrel in that twist. Quote Link to comment Share on other sites More sharing options...
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