I called TB in Cheyenne and they told me to bring the rifle and suppressor so they can examine both. Long story short, they found the collar on the barrel was not "square". They machined it correctly and life is good now. They told me that they see this issue a lot.Do you think it was clearance and gas pressure or barrel harmonics? I've never run into an accuracy issue shooting sub caliber through my 30 cal suppressor.
Also how long is your 300 win barrel?