Never try to check a tight bore with a caliper. This is bullshit and I know what I'm talking about it's my job
:P you need to be way more accurate to ckeck a barrel who as a .01mm tolerance
Originally Posted by L473ncy
Forgot what TN stood for but it's also known as a "TBB" (Tight Bore Barrel) and I'm pretty sure they're interchangeable. Also best to verify the inner diameter with a digital calliper.