Supersonic Gas Port Size???

[abyssdncr]

I turned my M1S carbine into an 8" pistol last year and am looking at building another carbine upper for supersonic loads.

I plugged 3 deer with the carbine barrel and got my first with a/the pistol last week using 155 gr. Amax loads. I'd like to get the kiddos started in centerfire shooting & deer hunting with the Whisper in a carbine upper using 125 gr. loads.

I'm looking at a 16" 1-12 twist barrel with a mid-length gas port, but my barrel maker is inquiring as to gas port size. Anyone care to make a suggestion?

Thanks,
:)