i gave opening up the barrel port in my 10" 1377 barrel this morning using a 5/32" drill. my drill press handled it just fine. i didnt have any kind of wooden dowels or anything that would fit so just had to do it as slowly/gently as possible. most of the burr flaked off then i finished with 400 grit followed by 800 grit. i pushed in a pellet then pushed it back out and inspected it. seems to go in smooth and removing it doesnt show any scratches or nicks from any burr. looks like i will be able to do this but i am going to have to research and invest in much better drill bits before i try this on my LW barrel.
Put a thin O-ring on top of your TP.Also around behind the probe O-ring, as it will lock your cocking handle so much better and give you an improved seal.
The O-rings for these aforesaid reinforcements are very thin (thread-like) and small.
Sounds like you have the situation well in hand.Shouldn't be a problem to get a good amount over 500 FPS.Keep in mind that without the barrel there is no resistance so you may need the power adjuster when the gun is complete.
Nice job, Robert. Those are excellent numbers. Sorry I didn't get back with you sooner on the spring question, but it looks like you have it sorted out!Wyo
I am wondering how far forward of the TP hole should the pinning hole be drilled? Center to center of course.