Locating gas port on an AR-15 barrel ?

[hoz53]

I am looking for info on how to locate the gas port/hole in ar-15 barrels. I have found some information. Of coarse the main thing is I want to locate it so standard length gas tubes will work.
----------------- Barrel length--- Port distance

Pistol. -------- Less than 10--------4

Carbine------------ 10 to 18------------ 7

Mid length------------ 14 to 20 ------------ 9

Rifle. ------------------ 20+ -------------- 12

Measuring my ar-15s they don't appear to be located very close to these lengths so that's why I am asking. Also where exactly do you measure from? Front of barrel nut threads on upper? Thanks Hoz

 

[Fast14riot]

Rifle length gas is 12.625" from back edge of extension shoulder. Gas journal shoulder to extension shoulder should be 12.125".

 

[hoz53]

Rifle length gas is 12.625" from back edge of extension shoulder. Gas journal shoulder to extension shoulder should be 12.125".

Thanks fast14 -- that's exactly the info I was looking for. Will rifle length be ok for a 16" barrel? I know I have one on an 18" barrel.

 

[Fast14riot]

For a 16", no rifle will not be a good choice, mid length is about perfect and will not beat up your brass or action. I'll see if I can dig up the shoulder location for mid length. IIRC gas port is typically 0.300" forward of the gas journal shoulder.

 

[hoz53]

16" barrel most likely will have a carbine length gas port unless you are planning to have a custom barrel made. In which case I would recommend a low profile gas block that fits under a free floating rifle length hand guard to protect the gas tube. If using an adjustable gas block, the hand guard will have to be shorter to expose the gas block.

Thanks Ledd. I will get the mid length dimensions and use them.

 

[hoz53]

For a 16", no rifle will not be a good choice, mid length is about perfect and will not beat up your brass or action. I'll see if I can dig up the shoulder location for mid length. IIRC gas port is typically 0.300" forward of the gas journal shoulder.

Thanks fast14-- I will use the mid length on the 16" barrel. The .300 is good to know. I appreciate any dimensions you can supply me but I don't want you to have to spend to much time or effort finding it for me. You've pointed me in the right direction. Thanks

Update-- I've found some info that shows a mid length gas system. Barrel shoulder to journal shoulder 8.75 + .300 to gas port.