So, I picked up a 3.5" Copperhead barrel off the EE with the intent of having it threaded and having a nice tuck setup. When I got the barrel, I put it on the gun took it to the range and tested it at 25 yards. Golf ball sized groups! Perfect! When I got it back from threading, it shot equally as well without a suppressor. But when I put my Tirant 9M on, it turned into a shotgun. Litterally... groups sometimes up to 10ish", but strangely still produced perfectly round holes.
Tried different bullet weights (115-147) and different powders (Titegroup to Longshot) to no avail. Have an TBAC Fly 45 that I'm waiting on a stamp for and luckily the FFL has a range on site. Well, everything shoots as well through the Fly 45 as it does without a suppressor (and sometimes better). I think the back pressure in the Tirant 9M is causing the bolt to unlock and unseal the case too early, and that this is causing erratic velocities. Haven't put it over a chrono yet, but that's my hypothesis.
The Tirant 9M has always lived on the MPX, so I'd kind of like to get it running in this barrel if I can. The gas port is already only ~0.055" (judging with gauge pins on angle). The barrel is only 3.34", so I'm not sure if there's enough room for the long ILWT adjustable gas plus that goes down to 0.040". The short version isn't compatible with this barrel. Not sure the fixed 0.0469" plug is going to do much over the existing 0.055" hole. Wondering if anyone else makes a fixed restricting gas plug that isn't long and fits a Gen 2?