[tahunua001]

overbore, and I might not even be using the term correctly but how I define it as your guns bore is larger than the diameter of the bullet passing through it.

basically how your guns conversion to 30-06 works is that they took the original barrel, chambered for 7.7x57mm and took a lathe to it and bored out the chamber to accommodate a 7.62x63mm casing. however since a lathe can only make holes bigger and can't make them smaller your barrel bore is still 7.7mm even though you're shooting a 7.62mm bullet out of it. even though 30-06 is a larger case, it's a smaller bullet.

in inches, 30-06 is a .308 diameter bullet but your barrel is designed to shoot .311 bullets. the 0.003 inches difference wont cause any serious safety issues but it will prevent the rifling(especially with an arisaka as they used microgroove rifling) from properly engaging the sides of the bullet and stabilizing it in flight, making it less accurate.