AR gas length

[Swang]

 

Purchasing a barrel,

16" barrel with a mid length gas system and another 16" has a carbine length.

What is the deciding factor?

Always thought 16 was midlength, and under was carbine

Never built an upper and thinking about things, always purchased complete uppers.

Edited February 19, 2022 by Swang
Clarity

[bobsguns]

Can't go shorter than 16" w/o doing a SBR tax stamp. 

I always thought 18" was mid-length & 16" was Carbine? Every dealer uses their own terminology it seems these days.

My .o2

[Chucktshoes]

A midlength gas system is my preferred setup on a 16” or 14.5” barrel. It is the sweet spot for recoil, reliability, and parts wear. Shorter than that and you need carbine for reliability, longer than that and the rifle length gas system is of course the best because Saint Eugene knew what he was doing. 

[Swang]

Thanks everyone

[Capbyrd]

On 2/19/2022 at 12:29 PM, bobsguns said:

I always thought 18" was mid-length & 16" was Carbine? Every dealer uses their own terminology it seems these days.

My .o2

This is inaccurate. 

Barrel length and gas system length are not directly related.   There are some rules, like don't run a rifle length gas system on a 12.5" barrel, but for the most part, you can find different systems on different barrel lengths. 

The truth is, a properly tuned system will work no matter what system you chose and what barrel length you chose. 

 

carbine barrel - 16"

rifle barrel - 20"

 

 

 

 

pistol gas system - 4"

carbine gas - 7"

mid-length gas - 9"

rifle length gas - 12"

 

 

Gas port size, gas port location, buffer weight and buffer spring are each a piece of a formula used to tune the gas system of a well built AR.  A good builder will measure the gas port of the barrel that he has and use that to help determine buffer weight and spring combos.  

Here is some information from SOLGW about gas ports.  They include what they use and what the TDP calls for.

 

Quote

Many companies won’t publish this. We believe in transparency. Whether you purchase directly from us, our dealers, or build it yourself, it all starts here…

SOLGW GAS PORTS:

10.5″ Carbine .073
11.5″ Carbine .071
12.5″ Carbine .068
14.5″ Carbine .0625
16″ Carbine .0625
13.7″ Mid .0785
14.5” Mid .077
16″ Mid .076
18″ Rifle .0995
20″ Rifle .093

Textbook TDP GAS PORTS:

MK18 10.3” Carbine .070
M4 14.5″ Carbine .0625
MK12 18” Rifle .0995
M16 20″ Rifle .093

SOLGW recommended Sprinco spring/buffer combination based on type of buffer system:

11.5” Milspec: Blue Spring/H2 (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)
12.5” Milspec: Blue Spring/H2 (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)
13.7” Milspec: Blue Spring/H (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)
13.9” Milspec: Blue Spring/H (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)
14.5” Milspec: Blue Spring/H (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)
16” Milspec: Blue Spring/H (LAW Folder H), A5: Green Spring A5H2 (LAW A5H1)

 

Edited February 21, 2022 by Capbyrd