I have a 16" Barrel with Gas port int he Carbine position and the hole is opened up to .125"
I have only been able to get Subsonic rounds to cycle using IMR 4198. Which is very similar to the AA 1680 and Lil Gun. Using 165+ grain projectiles. Cannot get the 150 grain or lower weight bullets to cycle subsonic with the current gas port configuration.
Going to the Pistol Position port will allow for a wider range of powders and bullets weights to be used for sub sonic.
Maybe you can get them to drill both holes and then tap them both for threads and use a small Allen screw to block one off?
http://www.nextag.com/CR-LAURENCE-CR...0FE71582A128DF
Don't screw into deeply though !!
I would say go carbine position for both Sub and Super. Just know that powder and bullet choices will be a bit limited.