Can someone tell me the correct diameter for a gas port on an AR15 barrel based upon the following barrel lengths:

20"
14.5"
10"
6"

or are they the same diameter regardless of barrel length? Thanks in advance.  

[url]http://www.ar15.com/forums/topic.html?b=3&f=12&t=145492[/url]

This one will answer most of your question.

Thanks GunCat !

This I received from another member:
'0.086-0.095" for the 10.5"
0.080-0.086" for the 11.5"
Start at .070" for the 14.5/16" barrels'
What might be a way to go  is to start at 0.060" and see if there is enough gas to cycle the action,if not try increasing size by 0.010" increments until it does.                     You will need to know where to drill the hole to position the front sight correctly.I have only the following which relates to shorty style hanguards.
'From the barrel nut side of the barrel       extension flange 178.5-180mm.'
Can anyone tell me where to position the gas port for correct mid length hanguard fitment?

Thanks FAHR451.