Lets talk AR gas systems and barrel lengths

[Lazarus]

This isn't a about pricing or availability but I need to be educated on different gas systems, length of gas systems, and barrels. I've always like the look of the regular 16" barrel carbine length (is that the right term) ARs but researching lately I see that BCM has a Recce where the barrel is 14.5" with a 1.6" flash hider pinned. That model has a mid-length gas system. In comparing the two I've found that with a 14.5" you gain a little in maneuverability and less weight but you sacrifice a little on velocity. How does the carbine and the mid-length gas systems differ though? I'm a newbie so I don't even know what the purpose of the gas system is.

 

[ActualArms]

Middy has less recoil generally and also usually a little more accurate. Here is my guide to ARs a gas systems.

14.5" and Less - Carbine
16" - 18" - Mid
18"+ - Rifle

However I heard 14.5 Middys are pretty nice too. I've personally never handled one.

 

[maxpaynya]

Gas system length and barrel length are not one in the same, you can have a rifle length gas (12 inches) on a carbine (16 inch) barrel just as you can have a carbine length gas (7 inches) on a rifle length (20 inches) barrel. What it boils down to is timing, the longer the gas system, the longer it will be before your bolt unlocks and moves to the rear. Spring and buffer weight come into play as well. Gas system lengths are as follows.

7" Carbine length
9" Mid length
12" Rifle length

If your gas block can fit on the barrel, you can have that length gas.

 

[Lazarus]

Gas system length and barrel length are not one in the same, you can have a rifle length gas (12 inches) on a carbine (16 inch) barrel just as you can have a carbine length gas (7 inches) on a rifle length (20 inches) barrel. What it boils down to is timing, the longer the gas system, the longer it will be before your bolt unlocks and moves to the rear. Spring and buffer weight come into play as well. Gas system lengths are as follows.

7" Carbine length
9" Mid length
12" Rifle length

If your gas block can fit on the barrel, you can have that length gas.

Yea I didn't think they were the same thats why I said gas systems AND barrel lengths. I just really wanted to the differences between to the two gas lengths. Also if anyone has any thoughts on the differences between a 14.5" and 16" barrel?

 

[maxpaynya]

you are going to get a minor amount more velocity out of the 16" barrel (200fps +/-) with the 14.5 if the flash hider (minimum 1.5") is not pinned on you will have to register it, not the case with the 16". I'm sure you already knew this.

 

[mtdawg169]

Gas systems are comprised of three components, all based on the barrel specs.

1) system length - carbine, midlength and rifle
2) gas port size - determines the amount of gas allowed to bleed off into the carrier for function
3) barrel length - determines dwell time based on distance from the gas port to the muzzle.

It used to be that you had two choices for gas system length, carbine (7" ) and rifle (12" ). As AR's gained in popularity over the last decade, someone figured out that you could reliably extend the system on a 16" barrel to 9". This accomplished a couple of things. It reduced pressure in the system, provided a softer recoil impulse and theoretically improved reliability due to less bolt breakage, which 16" carbine gas systems were notorious for.

Enter Knights Armament Company in approximately 2008. They introduced a proprietary intermediate gas system length on a 16" barrel which is approx. 11" long. The intermediate gas system, provided a much softer recoil impulse than even a midlength due to more pressure reduction and less dwell time. Dwell time is the time it takes a bullet to pass the gas port and exit the muzzle. KAC developed the E3 gas system along with an improved bolt design to greatly increase parts longevity, namely the bolt. At the same time, they produced a very flat and soft shooting gun. Downside, the gas tube is proprietary and not commercially available.

A couple of years went by and BCM decided to try something similar to the KAC system, but with the commercially available midlength gas system and introduced the 14.5" midlength. The 14.5 midlength operates on the same principal of reduced dwell time, but uses the more readily available 9" gas tube. The downside is that you will have to pin the muzzle device to achieve a 16.1" barrel length unless you own an SBR.

I'm a big fan of midlength and intermediate gas systems and would recommend a midlength for anything over 14.5" up to 18". Just be aware that the 14.5 midlength guns typically require higher quality ammo, as some steel cased or cheap brass ammo is on the low end of the .223 pressure spectrum. The lower pressured ammo, combined with a system designed around 5.56mm pressure ammo, can sometimes short stroke due to inadequate gas pressure.