Bill,
OK I did check the barrel at about 2" down from the muzzle and it is .287"-.288" The throat and the beech end of the barrel shows some wear but amazingly the upper 2/3rds of the barrel is pretty tight to Mil spec! I too do not worry about groove diameter I with Ian on this;
"I'm interested in are headspace, chamber diameter at the breech end, neck diameter and taper, throat freebore/size/length/angle/shape, what the transition looks like between chamber and throat, and bore diameter ahead of the throat."
Most times a pound cast is the only thing I need to set up a rifle for shooting cast!
With this rifle however I needed a lot of info on the chamber since I have to make the cases!
The Japanese Service specs are pretty different than SAAMI Specs ( Will post a comparison below)
I would love to have the Japanese Service Chamber specs but I can not locate them.
I have found that I have best results with .243 Win brass Run through a Special Swage die ( Thanks to Brad) that reduces the head size to close to proper diameter for the 6.5 x 50 I still find on some brass I have to spin it up in my drill press and reduce the size a tad more because of "spring back" I thought of actually annealing the "whole case" first because pressure is not an issue with the loads I shoot. But IO figured most folks think I'm crazy enough! (Actually if the heads were annealed and fired with my light loads they world work harden after about 2 firings!) And save a lot of wear and tear on my arm, press & swage die!) I have a set of old Pacific 6.5 x 50 dies The FL sizer bring the cases to SAAMI Spec which is "Small"
Once the cases are blown out I do not resize them. I have turned the case necks just enough to fit the chamber with the .277" cast bullets
So that the loaded cartridge has very little tolerance in the neck upon chambering!
The only problem I see is that that Little Lee 135 gr bullet needs to make the jump into the chamber ( I have yet to find any cast bullet that can be loaded in the case and still touch the lands) All in all the Lee bullet seems to work well. so no since spending more money if I don't have to!
Jim