Carbine length gas system

[Robin]

I have read here that a carbine length gas system is no good. Mek has noted this many times and I'm interested to know why. I'm thinking of making a .223 Wylde upper and most of the barrels in the length I want are 'carbine length gas system'. I can't seem to find any information as to why this is a bad choice. I don't want to waste my time and money on something that will not function reliably, so any information and or sites with information would be greatly appreciated.
Robin

 

[BDinPutnam]

What length barrels are you looking at?

 

[Robin]

16" The only information I can find says it might be a little harder on the bolt which can be remedied with a heavier buffer, and the negative's for that system arise from the military using it on full automatic. Obviously I will not be operating in that mode.
Robin

 

[redtail]

Never had an issue with 16” carb length gas, mid length recoil might be perceived as softer though.

 

[kev74]

All of my ARs - a couple of .223/5.56 and a 7.62x39 - have carbine length gas systems. I havent had any issues with any of them.

 

[ManrisFrack]

@meketrefe

My understanding is that it's tougher on the action components. Gas gets directed back the action earlier in the firing process while the pressure is higher. Results in a quicker, more forceful cycling generally (of course you can still use an adjustable block or gas key and mitigate this).

You can still build a reliable rifle on carbine gas - tons of examples are out there.

 

[Robin]

Awesome, thank you fellows!!! You guy's never fail to deliver!
Robin

 

[JamieZ]

Carbine length gas system,,,,first AR I built,,,,have fired many rounds through it. All parts still work like its brand new. Gun has to be 25 years old.

 

[togmaster]

JSE Surplus should have 16" mid length barrels. The one I have came from RRA.

 

[Marine Cpl]

Not mentioning any names, but some people take numbers and figures too seriously. Carbine lengths have worked in millions of rifles despite mid length being better on paper. 16 inch .308’s have taken many deer despite 18 inch .308’s being better on paper.

Sometimes paper figures are just that. Paper figures.

 

[JamieZ]

Why would a 18 be better on paper then a 16? Are you saying 18's are more accurate? Or are you saying mid-length is more accurate than carbine?

Im lost

 

[Marine Cpl]

18’s have more velocity.

 

[meketrefe]

@meketrefe

My understanding is that it's tougher on the action components. Gas gets directed back the action earlier in the firing process while the pressure is higher. Results in a quicker, more forceful cycling generally (of course you can still use an adjustable block or gas key and mitigate this).

You can still build a reliable rifle on carbine gas - tons of examples are out there.

yes, it is tougher because for the gun to function ok with all potential civilian ammunition the gun may be over-gassed.
The guns might function ok for many but at that posting distance there is still a substantial amount of pressure and, unlike in a loose fit long
stroke system, it is much harder to balance the resistance of all components vs. speed.
On top when shooting in a DI there is a substantial amount of heat that goes directly into the bolt group so
the bolt gets very hot. it can be mitigated a bit with a pigs tail gas tube but that is not ideal.
It is not the same to build a gun for a specific set of ammo like for sporting use or target where there is no need for a carbine
porting ever and there is a huge difference in ammunition. For example, 55gr LC plan (nato spec) is about 300-350fps faster
that 223 PMC bronze out of the same barrel. So, some carbine ARs will have problems cycling these and other varmint light loads
or they will have to be over-gassed when firing the hottest ammo like some mil spec or match stuff.
The adjustable gas block might help but ends up being a pain if one is switching loads. Initially the best way to do it is to
increase the weight of the group to slow down the aperture. But ideally a mid port or rifle is a lot easier to balance.
Or in order to increase the reliability one might build a short piston carbine. My piston systems come with 3 positions that is full
open, suppressed and closed that is a quick turn at be base of the block. They are also more reliable for the most crazy conditions
including 'over the beach' type of abuse. But they are more expensive and a tad more heavy so there is always a bit of a tradeoff.

the ideal is to have a mid length or rifle length porting as originally intended and don't screw up with the AR like the Army did in order to
attach the M203 launcher.

 

[meketrefe]

Barrels are dirt cheap. Much more than the ammo so one might experiment but if one wants something a bit better thought out
these are some things that are proven to help in several ways and as needed:

- I prefer 18 that is ideal for a carbine but even a 17" or typical 16" is fine for 223. Like with any guns is good to have a good
sense of what is going to be the overall lenght and use because a 18" barrel with a 1 baffle (even more effective) type of short brake
might end up being shorter than a 16" barrel with one of those tacticool brakes they sell and you gained nothing, only lost speed.

-1 to 8 twist is ideal but many will do fine with 1:9 if they are not going to shoot the longest match bullets.

-1 to 7 is tight but if there is no 8 twist option better than going to 9 if match bullet shooting is a possibility.

-Stay away from carbine porting. Mid length or file length with proper porting always better. Consider if you want a long rail
for a dissipator barrel design. 18+rifle is great too.

- Also stay away from M4 tacticool cuts and pencil barrels with minor diameter too small ahead of the block.

- Instead a scout mid way profile is much better in terms of harmonics and heat distribution and one might even choose
a tad wider diameter with flutes ahead of the chamber as soon as the flutes are not too deep. it is better to have more
than to have them too deep and that also increases dissipation in this critical area. It has been demonstrated that M4 style
barrels can fail before the gas tube does and ahead of the gas block and for this very reason we stay away from stupid M4
profiles . there are so many other great options to choose from from budget to expensive. For example lilja introduced integrated
cooling flutes by request of the navy seals. Also they are a lot more accurate barrels than chromed mil spec barrels to start with.

-Another thing you might like is to get 5/8x24 threads no matter what gun and to prevent crown swelling over time.
1/2 threads are ok for the 20 bore but not for the 22 bore or anything larger.
Anything .338 and above should be 3/4 (that is why I did for the gunner) or even larger for the thumpers.

- Finishing is personal but I like nitrocaburized barrels in and out that is far superior to mil-spec and chrome. Of course make
sure the company does a good job like ARP and not the hack job some people do.

Again these things are considerations, not a totally must have.

These have been discussed, explained, tested and proven 1 millions times over but we have to keep reminders as we move
from forum to forum and people come and go.

 

[Xae289]

The theory with AR gas systems is that you want just enough gas in the system to reliably cycle the action 100% of the time and no more. More gas = more stress on the BCG and buffer system, and more dirty gasses going into the action, increasing your fouling. This will affect reliability if you let your gun go high-round counts without cleaning. It will also cause more wear on your buffer spring and bolt lugs over (a long) time. You will also have more recoil. A noticeable amount? Depends. The three ways to balance this that I can think of off the top of my head are:

1) Gas system length. The shorter, the higher the gas pressure in the gas system. The 5.56mm and .223 rounds you'll be firing through the Wylde barrel will probably be optimized with a mid length gas system if you want a shorter barrel or a rifle length if you want a longer barrel. In all reality, if it's all you can find, a carbine length will probably be fine and your rifle will probably work fine with one if you're just going to use it casually and aren't going to put thousands of rounds per year through it.

2) Gas block aperture size. An adjustable gas block can allow you to take an over-gassed system and tune it to give you that "just right" amount that cycles with 100% reliability, but no more. If you do go for a carbine length system, this would be a good upgrade. If you go for a mid- or rifle-length system, you probably don't need one, but it would still be a potentially useful upgrade.

3) Buffer weight. You can use a heavy buffer to slow down the bolt carrier group and buffer's movement to the rear if you do have an over-gassed system. This isn't something I suggest you mess with in building from scratch. This makes more sense if you didn't know anything about an AR gas system, bought an AR in 5.56 with a carbine length system and fixed gas block, then learn about the potential problems and want to correct your over-gassing issue without getting a new barrel or gas block.

So yea, you can get a proper gas tube length and adjustable gas block, pick a specific ammo and tune the gas system perfectly to it to have the rifle live up to its potential. You could also get a carbine length gas tube, call it a day, and it'll be good enough. Or take a middle ground like a carb length with adj block or a longer tube and a fixed block.

 

[gun_slinger_boy]

I don't want to waste my time and money on something that will not function reliably...
Robin

Carbine length is the MOST reliable. Over gassing yadi yadi yada. 99% of people will never shoot their rifle enough for that to even begin to be an issue.

 

[meketrefe]

So you get a new barrel and/or gas block and then what happens when the PMC bronze or varmint loads short-stroke?
Again the carbine porting can work fine but there is ZERO need or reason to go that way and it is like choosing to cross the river
via a tight rope vs a bridge. A lot harder to balance and loss versatility.
In fact the M4 is out of balance as it is designed and on top we are trying to apply to civilian ammo and use.
I see people buying gas blocks and then super light carriers, that is absurd unless one is tuning for a specific type of load.
It is like systems that are designed to shoot subsonic/suppressed that should be dedicated or with a switch.
I found the most reliable way to run a subsonic/supersonic rig is to have 2 gas blocks in tandem with a quick on/off valve each.
you don't want dedicated rifles then better have two ports.

 

[meketrefe]

Carbine length is the MOST reliable. Over gassing yadi yadi yada. 99% of people will never shoot their rifle enough for that to even begin to be an issue.

If one is not going to shoot their gun much and just for the occasional weekend bang bang I agree. Anything will do.
A 10/22 is also a great way to save money to shoot dinner plates at 50 yards.

This is more in case someone wants to put together a simple yet better AR and w/o breaking the budget.
The AR carbine with the carbine porting is the LESS reliable by design. It is not a totally bad system but it is not as good as
the originally conceived AR that evolved into the M16A4 and why improvements to the M4 have to be introduced
all the time including thicker barrels in this last war and still pretty out of balance.

Of course we cannot compare a service maintained gun with bottom barrel el cheapo kits parts but if one pays some
attention there are popular parts were every single civilian component is far superior to anything mil spec in the DI design and this
keeping the rifle withing a budget.

I am talking about the heart of the AR that is the DI group and barrel and w/o counting some of the other simple
options in terms of receivers and ergonomics that are also superior to mil spec.

 

[BDinPutnam]

Plenty of 16" middies available at the same price points as carbines.

No brainer in my book.

 

[Vapor]

Battlefied Las Vegas seems to do fine putting 10s of thousands of rounds through their carbines. Here's a shock, they say the premium PSA uppers and bolts last as long as anything else under FULL AUTO FIRE.

Mid length probably will show a longer life time. I'm not sure anyone on here puts enough lead downrange to notice.


Will you notice it? Well, do you plan to shoot the bore out of your rifle? You might notice then.


I have a two carbine , one mid, and a rifle. The rifle is a sweet shooter. I have a very heavy profile barrel on the 18". It needs an h2. Not really much softer than the carbines. Ymmv. I'm not running out to replace my carbines anytime soon.

 

[gun_slinger_boy]

If one is not going to shoot their gun much and just for the occasional weekend bang bang I agree. Anything will do.
A 10/22 is also a great way to save money to shoot dinner plates at 50 yards.

This is more in case someone wants to put together a simple yet better AR and w/o breaking the budget.
The AR carbine with the carbine porting is the LESS reliable by design. It is not a totally bad system but it is not as good as
the originally conceived AR that evolved into the M16A4 and why improvements to the M4 have to be introduced
all the time including thicker barrels in this last war and still pretty out of balance.

Of course we cannot compare a service maintained gun with bottom barrel el cheapo kits parts but if one pays some
attention there are popular parts were every single civilian component is far superior to anything mil spec in the DI design and this
keeping the rifle withing a budget.

I am talking about the heart of the AR that is the DI group and barrel and w/o counting some of the other simple
options in terms of receivers and ergonomics that are also superior to mil spec.

yes, it is tougher because for the gun to function ok with all potential civilian ammunition the gun may be over-gassed.

To me this is the mark of reliability before you start messing with parts. Of course you can make anything more or less reliable depending on what components you use. What would happen if you had a 20 inch platform and a 16 inch platform that had all the same parts except for that extra 4 inches on the 20 inch? I'm talking barrels, BCGs triggers etc. Would the 20 inch really last that much longer/be that much more reliable? I don't think it would. Now what if we took a 16 inch platform and tricked it out with all the best components (civilian) and put it up against a bare bones 20 inch mil spec? Which would last longer? I bet the 16 inch would. I only say this to point out that it's obvious changing out components will lead to a more robust system. So then what are we left with? Which system will shoot more varieties of ammo. The 16 inch will shoot some pud ammo reliably that the 20 may not be able to.

ETA: I'm not knocking mid or rifle length gas in any way. Just pointing out that it's really nothing the average shooter needs to worry about. In fact I still want to maybe build an AR with a 16 inch barrel and rifle length gas system just because it's cool.

 

[scooter86]

Since you currently have a choice, I would look to go mid length. Shoots a little softer. Most of us aren't going to shoot enough to have long term reliability issues with carbine lengthn systems anyway. If you do, then the cost of a new barrel/gas system won't be a bitter pill to swallow. Carbine length is my oldest ar, I threw a h2 buffer in her and just shoot.

 

[dsdmmat]

@Robin straight pull bolt action AR. Why mess with gas when you can use your muscles to cycle it reliably.

 

[meketrefe]

ETA: I'm not knocking mid or rifle length gas in any way. Just pointing out that it's really nothing the average shooter needs to worry about. In fact I still want to maybe build an AR with a 16 inch barrel and rifle length gas system just because it's cool.

I think a 20" is not as practical but still ok for folks around the ranch or shooting varmints and/or target competition and
18" would be a better compromise between those two different objectives for a carbine.
And again, the issue is not so much with the barrel length but the barrel porting, profile and other considerations as described above.
The porting alone, with everything else the same makes the system more reliable and better balanced.
I guess for many people might mean little but if one wants to build the best possible carbine that has a lower chance
of failure under any circumstances those directives can be considered. And it is not that we are talking about spending
a lot or super complex stuff, simply a different set of choices that divert a little from the main stream tacticool fashion that
somehow got established in the marketplace.
One can buy barrels much cheaper than ammo so this is not the issue. The issue is getting the most of ones carbines while we use them.
for the same reason I would go for a better beefed up bolt vs. a mil spec one since the difference is what 20 bucks?? so it is a matter
of having something better for comparable budgets. IMO There is just no good reason for a civilian not to get a better AR by design.
It is all a matter of priorities and notice I am just talking about those critical components and nothing receiver or ergo related
that can be subjective.

So to summarize, plus a few other things, and again...
all these things are optional considerations, nothing else:

-Stay away form carbine ported barrels. Mid lenght or rifle length porting is better no matter what size of barrel.
-Stay away from any sort of early M4 cut or profile or pencil barrels. Minor Diameter is too small ahead of the chamber.
-1:8 twist works great with all the bullets the 223 can shoot. 1:9 will work for those who do not plan in shooting any long bullets
like the longest match bullets or like a solid 70gr like barnes TSX taht needs an 8 twist. If uncertain and you don't have an 8 twist
then go with the 1:7 twist and make sure you don't want to shoot light varmint hyper-velocity rounds wtih thin jackets that might come apart.
- 3R and some polygonal rifling is a good choice for the AR specially for shooting long bullets or solids as they are smoother. Lothar walter or
pac-nor(Also Noveske) are the best. Stay away from the blackhole weaponry as they are a hit and miss making barrels.
-Stay away from 1/2" threads and use standard 5/8 up to 30 caliber. with 338 calibers go to 3/4" or beyond there with thumpers. 1/2" threads
are ok up to 20 caliber but not for 22 caliber and this is not critical but might prevent crown swelling over time.
-A scout medium-light type of profile is a good way to have a more robust barrel that doesn't change so much as it heats up. A wider
profile can have flutes in the middle ahead of the chamber that is a great way to add reliability and accuracy. It is better to have shallow flutes
and more flutes than any deep flutes and stay away from exotic designs like spiral flutes that serve no purpose and there is no way to guarantee
outcome since the alloy stock cannot be stressed relieved after the cut.
-Finishing is a personal thing but personally I think there are benefits to stainless (just brushed) or having the barrel nitrocarburized
in and out that is a much better and accurate outcome than chrome bores and/or chambers.

-I also like to order an enhanced bolt like the ones offered by ARP or young manufacturing that not only have increased radius at the lug
base but are also made of harder steel with a proper heat treatment so they are about 20-30% stronger than mil spec bolts. you can get
a JP bolt but there is no need to pay more.

-Of all the extractors I think the best batches have always come from Armalite. I never had an armalite extractor break even with alternative
calibers and 7.62x39 extractors for some pretty hot stuff like the 6.5BR.

-Always get a steel gas block that is thigh and avoid set screw and go for a well made strong clamp type as those provide the best seal
and harder to move other than mil spec pinned turrets that are also heavier. don't Micky mouse with aluminum or set screws and fancy designs. Same way get a decent gas tube that is tight and well installed. No initial need for adjustable blocks and fiddling if the porting is up to spec.

-GEt a M16 style carrier and as soon as it is well installed and key stacked and mil spec will work just fine. stay away from AR15 carriers and
Aero super light carriers that serve no purpose and only open the door to get the system more out of balance. Initially there is no need for other buffer or spring if it is up to spec.

- 2stage RRA trigger with a bit of conditioning of the springs and breaking in, can be tuned to work like the most expensive 2 stage triggers. GMMC is optional. personally the RRA is better at least for me.

Other considerations:
- There are lowers that have integral trigger guard and a bit more meat ahead of the mag well so that is good to avoid damage against barricade.
- The weakest point of any AR floating or not floating is the shank area in the upper receiver. So if you have some hand-guards see if you
can couple the top rail of the hand-guard with the actual receiver rails. For this you might use a simple and inexpensive coupler with a couple of allen screws. It is not a lot but it helps support the hand-guard under load like when shooting prone a bit downhill that you might lean with
extra weight against the stock and tripod or support. NEVER, EVER use the scope mount or rings to couple this two pieces. The coupling should
not touch anything in contact with your glass/sights. We actually measured this with calipers by putting a shooter and putting pressure and the coupling reduced the flex but a 2 or 3 thousands.

- When choosing optics mount about the two piece side to side rings and instead use the top bottom and the bottom being integral to the mount. Also avoid long cantilever as those will be more susceptible to its own torque force from usage and small impacts. Instead a short
cantilever is much better just to avoid the rails and/or coupling.

what else we are missing?...

 

[Fightingfish]

I think a 20" is not as practical but still ok for folks around the ranch or shooting varmints and/or target competition and
18" would be a better compromise between those two different objectives for a carbine.
And again, the issue is not so much with the barrel length but the barrel porting, profile and other considerations as described above.
The porting alone, with everything else the same makes the system more reliable and better balanced.
I guess for many people might mean little but if one wants to build the best possible carbine that has a lower chance
of failure under any circumstances those directives can be considered. And it is not that we are talking about spending
a lot or super complex stuff, simply a different set of choices that divert a little from the main stream tacticool fashion that
somehow got established in the marketplace.
One can buy barrels much cheaper than ammo so this is not the issue. The issue is getting the most of ones carbines while we use them.
for the same reason I would go for a better beefed up bolt vs. a mil spec one since the difference is what 20 bucks?? so it is a matter
of having something better for comparable budgets. IMO There is just no good reason for a civilian not to get a better AR by design.
It is all a matter of priorities and notice I am just talking about those critical components and nothing receiver or ergo related
that can be subjective.

So to summarize, plus a few other things, and again...
all these things are optional considerations, nothing else:

-Stay away form carbine ported barrels. Mid lenght or rifle length porting is better no matter what size of barrel.
-Stay away from any sort of early M4 cut or profile or pencil barrels. Minor Diameter is too small ahead of the chamber.
-1:8 twist works great with all the bullets the 223 can shoot. 1:9 will work for those who do not plan in shooting any long bullets
like the longest match bullets or like a solid 70gr like barnes TSX taht needs an 8 twist. If uncertain and you don't have an 8 twist
then go with the 1:7 twist and make sure you don't want to shoot light varmint hyper-velocity rounds wtih thin jackets that might come apart.
- 3R and some polygonal rifling is a good choice for the AR specially for shooting long bullets or solids as they are smoother. Lothar walter or
pac-nor(Also Noveske) are the best. Stay away from the blackhole weaponry as they are a hit and miss making barrels.
-Stay away from 1/2" threads and use standard 5/8 up to 30 caliber. with 338 calibers go to 3/4" or beyond there with thumpers. 1/2" threads
are ok up to 20 caliber but not for 22 caliber and this is not critical but might prevent crown swelling over time.
-A scout medium-light type of profile is a good way to have a more robust barrel that doesn't change so much as it heats up. A wider
profile can have flutes in the middle ahead of the chamber that is a great way to add reliability and accuracy. It is better to have shallow flutes
and more flutes than any deep flutes and stay away from exotic designs like spiral flutes that serve no purpose and there is no way to guarantee
outcome since the alloy stock cannot be stressed relieved after the cut.
-Finishing is a personal thing but personally I think there are benefits to stainless (just brushed) or having the barrel nitrocarburized
in and out that is a much better and accurate outcome than chrome bores and/or chambers.

-I also like to order an enhanced bolt like the ones offered by ARP or young manufacturing that not only have increased radius at the lug
base but are also made of harder steel with a proper heat treatment so they are about 20-30% stronger than mil spec bolts. you can get
a JP bolt but there is no need to pay more.

-Of all the extractors I think the best batches have always come from Armalite. I never had an armalite extractor break even with alternative
calibers and 7.62x39 extractors for some pretty hot stuff like the 6.5BR.

-Always get a steel gas block that is thigh and avoid set screw and go for a well made strong clamp type as those provide the best seal
and harder to move other than mil spec pinned turrets that are also heavier. don't Micky mouse with aluminum or set screws and fancy designs. Same way get a decent gas tube that is tight and well installed. No initial need for adjustable blocks and fiddling if the porting is up to spec.

-GEt a M16 style carrier and as soon as it is well installed and key stacked and mil spec will work just fine. stay away from AR15 carriers and
Aero super light carriers that serve no purpose and only open the door to get the system more out of balance. Initially there is no need for other buffer or spring if it is up to spec.

- 2stage RRA trigger with a bit of conditioning of the springs and breaking in, can be tuned to work like the most expensive 2 stage triggers. GMMC is optional. personally the RRA is better at least for me.

Other considerations:
- There are lowers that have integral trigger guard and a bit more meat ahead of the mag well so that is good to avoid damage against barricade.
- The weakest point of any AR floating or not floating is the shank area in the upper receiver. So if you have some hand-guards see if you
can couple the top rail of the hand-guard with the actual receiver rails. For this you might use a simple and inexpensive coupler with a couple of allen screws. It is not a lot but it helps support the hand-guard under load like when shooting prone a bit downhill that you might lean with
extra weight against the stock and tripod or support. NEVER, EVER use the scope mount or rings to couple this two pieces. The coupling should
not touch anything in contact with your glass/sights. We actually measured this with calipers by putting a shooter and putting pressure and the coupling reduced the flex but a 2 or 3 thousands.

- When choosing optics mount about the two piece side to side rings and instead use the top bottom and the bottom being integral to the mount. Also avoid long cantilever as those will be more susceptible to its own torque force from usage and small impacts. Instead a short
cantilever is much better just to avoid the rails and/or coupling.

what else we are missing?...

It’s not my thread, but I wanted to thank you for posting this detailed reply. I’m building my first AR, and there is a ton of great info here!

 

[Podmonkey]

Mid-Length vs. Carbine

The M4 carbine has a 14.5" barrel and a ‘carbine’ gas system, meaning the gas port is at the 7.5" mark. Civilian clones of the M4 usually have 16" barrels for legal reasons, but traditionally...

www.guntweaks.com

@Robin, what manufacturers are you shopping? Midlength gas on 16" are as common as white bread now. What is your intended purpose for the rifle? For general use I'd recommend either Faxon or Ballistic Advantage both of whom offer a quality, accurate barrel at a good price. Both offer a plethora of mid length gas options. I have a 14.5 pinned barrel w/ mid length from Ballistic Advantage on the NYGF build and I have been very happy with it. Several thousand rounds through it now.