This is no "harder" data than that which you get out of a bore with a wall thickness gauge. Not just recs or specs. Is there any particular make, model, gauge, era of gun about which you wish to know the numbers before the cone? I've always just gone by Pipes' "90 thou is acceptable and a tenth is better". Course the 9" from hither and yon could also mean something as 9" from breech is getting out there toward the forward hand. 9" from muzzle? What could it matter as many modern target shotguns are perfmetal out there anyway?
jack
