After balking for years I have finally decided to build my first ar pistol !
One thing however that seems to be a matter of some disagreement is the size of the GAS PORT HOLE in the barrel. My plan is for a 7.5'' barrel of
"hbar" profile,,,, and let me say I turn , port and proflie my own barrels . For this build I am planning on useing a kreiger match ss 1 in 7.7  .
I have talked with many ar pistol shooters and shot many but none have too much of an idea of the current consensus as to the size of the hole .
    Various pistol barrel producers use slightly diffrent size holes I am told and there seems to be an argument as to the port hole size vs. functionality
as well as the relationship between the hole size as it relates to 7.5'' barrels  and up to the longer pistol barrels . ALL the many other barrels I have
"made" have had ZERO reliabilty issues as I have tried to do as much research as practical for the length of barrel , gas port location etc. some
have had nonstandard   port size as well  ..........any help in this area from some of you out there that are in the know or just have an opinion will
be greatly appreciated .............................................................................................IRONSIGHTRANGER

All depends on the barrel and other factors like the BCG, buffer, ect...
I'm building a 7.5" with Rainier Ultra Match barrel. The port is about .056. That seems real small to me but guys that have them say they run.
My last 7.5" was opened to .078.
I would use .070 as a start.

I'm with SC, around .70, that said while a tad bit of a pain it sure is easier to start small and work yourself into the size that ultimately works for your pistol.

THANK YOU FOR THE INFO
A few folks have commented on the smaller hole be the "correct" solution " and I have taken in the factors you mention into consideration .  
as in under .075 , A good friend has an arpistol built by a  builder of great experience in this and I am planning on using his style of buffer.
A regular rifle length tube (spikes tactical style I believe) with a carbine buffer and a rifle spring cut to 9 1/8"  this thing is flawless so far with many rounds of various bullet weight, charge etc. BUT HE STILL WONT LET ME TAKE IT TO BARE BARREL TO CHECK THE HOLE . thanks again

If it's too small it will be under gassed and won't cycle. Rainier says their gas port is proven so I have to believe it's something to do with the barrel itself. I had a DPMS kittycat barrel that was in the mid 60's. It had to be opened up.