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Who has the low down on gas ports for different length barrels? My main interest is 10.3 and 11.5 barrels but if you have a chart or list of other lengths that would be great. I have an old barrel I'm having cut down so it needs to be opened up so it will run.
TIA for the help.
14.5" and 16" barrels run .062" IIRC 10.3" and 11.5" are .085" and 12.5" is .074"Quote:
Originally Posted by Boom
Moose thank you.
Heres a good list. Scroll down about halfway.
http://groups.msn.com/TheMarylandAR1...tenacefaq.msnw
Quote:
Originally Posted by Thors ~ Hammer
I wouldn't use that list. I screwed up two barrels following his recommended port sizes. He's got the ports for a 14.5 inch barrel way too large. .61 - .62 is the perfect size for a 14.5 inch barrel, especially if you're running fullauto. On an 11.5 inch barrel go with .69 IIRC, no larger.
Bump...
Where exactly is the gas port located. I am thinking inside of the carrier key.
Could not find any diagrams with this info.
Factory 10.25" CQBR barrel 1x7 .091"
My AR15Barrels cutdown 10 7/16" LMT (cut down from a factory 14.5") 1x7 .078"
Quote:
Originally Posted by Colt6920
6920,
The port is in the barrel under the gas block (or front-sight base) and is what bleeds gas through the gas tube back to the carrier key.
Which one runs smoother? ;)Quote:
Originally Posted by gotm4
I'll let you know but I'm sure it's my LMT. ;)Quote:
Originally Posted by AR15barrels
My buddy is drowning in the Colt koolaid but DAMN that make the gas port HUGE!
LMT's 10.5" barrels come 0.071" which is done that way to use with a can.Quote:
Originally Posted by gotm4
If someone is not going to run a can, I usually open them to 0.076"
With your liking of the heavier buffers, I make yours 0.078" ;)
If someone was to want to stay with a regular cabine buffer, I would go 0.073" and call it good.
Quote:
Originally Posted by AR15barrels
Good info. Thanks. :D
I think my buddy is going to run a Colt X buffer in his. Right now he has a H3 but hasn't fired it yet and will be using a SureFire 556K suppressor. No wonder why SAW recommended the X buffer.
Gotm4 and I fired our rifles side by side the other night. Mine is the Colt cqbr barrel with the .091 gas port and an H3 buffer, gotm4's LMT has the .078 gas port with an H2 buffer I believe. Side by side, they felt very similar to me. I think gotm4 will agree. It was actually pretty suprising considering the differences in our setups.
AR15barrels, any idea why Colt chose such a large gas port on their factory cqbr barrel?
I havn't fired my rifle suppressed yet but will soon. According to Specialized Armament Warehouse, the X buffer is necessary to run my rifle suppressed so the thing won't tear itself apart. I really don't want to go that heavy with the buffer but I also don't want to do any damage to my rifle. Any opinions?
Pat,
I think they feel similar for a few reasons:
Your barrel is a heavier profile barrel. (Mine was a factory 14.5" LMT...read light same as a Colt 6921 M4 profile before shortening to 10").
Your buffer is heavier.(a tad over 1oz heavier, H3 is 5.6oz, H2 is 4.57oz).
Your suppressor mount/muzzle device works a little like a comp/brake. (My AAC Blackout really doesn't do much, I can even see flash with XM193 and it's timed with 1 port facing downward 6 o'clock. Actually when I changed from the original M4-2000 Mod 07 mount which is like a Phantom I immediately could feel more recoil with the Blackout)
You were shooting PMC 55gr FMJ. (I was shooting MagTech 55gr FMJ)
The difference our rails (my KAC RAS2), my FSB, vs. your now lo-pro pinned GB, 9.0 LR, X200 and LMT front sight probably even each other out.
When we compare them with suppressors we'll use XM193 to eliminate the ammo difference. I have a H3 too so we can see how that changes the feel when compared to my own H2.
Robb,
Agree with everything you said except concerning barrel profile. The Colt cqbr barrel is very light under the handguards. No thicker than yours and perhaps a bit thinner. My barrel is also ever so slightly shorter than yours.
Not easy for me to admit mine's shorter than yours but what's a brother gonna do?
Yeah I'm getting old I don't remember the exact profile.Quote:
Originally Posted by TacticalShooter
But I do remember that your barrel measures 10 1/4" and mine is 10 7/16", not much a difference normally but when you get barrels with that little bit of barrel past the gas port it can be very significant in getting enough gas pressure fast enough to cycle the action reliably but then to not have too much. It's a fine science to get it 'just right', if that even possible. Simply put the 10" guns are going to need close attention to preventative maintenance when compared to say a 16" midlength or a 20" rifle length AR. Everything has a 'service life' and the 10" ARs is shorter than most.
Due to larger port sizes required to run with such short dwell times, you really have to keep a watch on port erosion and correct for it by going to heavier and heavier buffers as the port enlarges.Quote:
Originally Posted by gotm4
As barrels get longer, the ports get smaller and dwell time becomes less critical.
That's why you don't see as much change over the service life of a 14.5" or 16" barrel as you do on shorties that are tuned to run right on the ragged edge of available dwell time.
I know this is a necropost, but I didn't want to make a new thread and I think this discussion could add to the sticky.
Basically I was wondering if someone can tell me exactly what length each gas system is? I've gotten multiple different answers to this question through my research, so I thought I would ask here. I'm really only inerested in carbine and midlength port locations, but for the sake of information, if you know them all, then list em :D
Can you be more specific? Your post doesn't make sense. Are you referring to the sizes?
Quote:
Originally Posted by Ironman8
There are multiple answers to this question based on what your refernce points are. From a simple perspective, carbine length handguards are 7", mid-length are 9". Gas port position would be slightly beyond the end of the HG.Quote:
Originally Posted by Ironman8
From Armalite's data, the length of their gas tubes for carbine and mid-lengths are 9 3/4" and 11 3/4" respectively. Note that the gas tubes extend rearward of the barrel extensions a bit, so from a HG perspective we're measuring from the delta ring forward, and from a gas tube perspective, we're measuring the length of the tube.
Finally, not sure if Armalite is consistent with the rest of the industry , and for that matter, while I'm under the impression that the industry has standardized port locations on carbine-length gas systems, I'm not sure if there's industry agreement on mid-length systems. I would need to hear from an industry SME regarding the latter.
Well I don't know how port LOCATION (not size) is measured, but I would logically think that the location would be measured from bolt face. I didn't include that in my first post, because I didn't know how they were measured (length-wise) and if there was even a standardization among the industry.
If they do measure from bolt face, then what I am looking for is:
The carbine gas port is 7.x" from bolt face
The midlength gas port is 9.x" from bolt face
....ect
I have seen lengths posted for the carbine gas system anywhere from 6" (which I know isn't right) to 7.8". This lead me to my question. Is there not a standardization?
There is standardization on the distance from the bolt face to the barrel extension's front face.
There is standardization of the distance from the barrel extension front face to the rear of the gas block seat.
There is standardization of the distance from the rear of the gas block seat to the center of the gas port.
Not all companies follow the standards.
If you added these figures up, you would end up with the following figures:
Carbine is 7.795" from boltface.
Mid-Length is 9.795" from boltface.
Rifle is 13.170" from bolface.
Thanks! PM sentQuote:
Originally Posted by AR15barrels
Well, necronecropost.
I saw this and I would like to touch on the GAS PORT sizes.
Not finding much, just general stuff. Here's what I'm thinking:
Cutting down a 14.5"DD (carbine?) to 11". So, I see what size. But it got me to thinking (dangerous). Is there a tried and true method for all barrels for porting? I am thinking there must be. I used the magic orange button, which usually answers all my questions, but I must be missing somthing. Not looking for the absolute, just a guide if i want to go shorter. Do it yourself sucks somtimes, as my funds are limited.
So in closing, HELP!
ETA: Suppresor added to the mix also. If my first question wasn't bad enough...