Start off with the block shut down, then slowly open/test the rifle. Once you get to the point that you are getting 7-10 foot ejections, then loctite the screw down. If you go for a dribble effect setting, then as the chamber/rifle starts to foul, the rifle will start to jam.
If your looking for a the cases to be ejected at your feet, start with the gas system set to eject around 10', lock the screw, then start to trim winds off the ejection spring. This will insure that the action is cycling at the correct speed, and the spent cases will stay on the bolt face a little longer to be ejected during the forward stroke of the bolt and not at the buffer stall.
At no time allow the gas port (oversized) to left wide open, even during any advice conditions. The excess speed of the carrier/buffer coming back is going to destroy the back of the receiver extension. If not caught in time, such as using a full length stock where your shoulder may be holding the butt stock in place (cracked receiver extension tube end), then the butt stock slips back away from the receiver extension, the carrier key is going to crack the back of the lower receiver off as the carrier/key tries to shoot out the back of the receiver, since the buffer is not being limited in it's rearward travel.
P.S. Why did you enlarge the gas port any way? Was there a cycling problem with the rifle/barrel, or is the barrel/port just oversized to test out a new gas block design?