Gunsmithing Gas port location

[cwshooter]

I've got a 7" pistol length gas tube for an AR 15 30-221 build. I have a JP adjustable gas block. I'll be profiling the barrel myself and installing the m4 barrel extension.
My question is where should the port go? Is there a standard distance versus the back end of the barrel, barrel extension, or the extension/barrel shoulder? Or am I targetting a specific length of protrusion of the tube into the the upper?
Thanks in advance.
CW

 

[skinnj1]

Re: Gas port location

PM me...

 

[cwshooter]

Re: Gas port location

done

 

[cwshooter]

Re: Gas port location

I found this on another forum:
"Length from bbl ext to gas block cut 3.6" . Gas port is .295" from gas block cut forward."
Sounds about right?

 

[cwshooter]

Re: Gas port location

Thanks to skinnj1 for some great info via PM.
CW