Avlane, I fired off all the factory ammo I had, just to get fire-formed cases, and then reloaded with the 0.268 Hornady seated out about as far as the original Carcano rounds were (OAL 75,25 mm, in my 91/41), to get the bullet as close up to the throat as reasonably possible. 1-1/2" groups at 100 meters with 28-30 gn of Reloder 15. No signs of overpressure. And don't forget the standard reloading tip for milsurps with chambers of uncertain dimensions - neck sizing only, using cases that have been fire-formed in the same rifle!

BTW, take a look at the tip of your firing pin under a watchmaker's eyeglass. It may be a trifle jagged. Not good for primers.

As to Arisakaicon: apparently (I do not have one) they have a Metford-style polygonal rifling, which has led to people thinking that the rifles were shot-out because they could not see any sharp edges! As a non-Arisaka expert, but a fairly experienced black powder shooter, I can tell you that polygonal bores are very sensitive to the size of bullet and its hardness.

Can you get hard lead bullets in varying diameters? Over here, for instance, there is a company called Rifle Bullet Caster GmbH & Co (Riflebulletcaster GmbH & Co.KG.) who make lead bullets with a Brinell hardness BHN 22 and diameters of 0.268/0.270/0.272" (weights 126/128/130 gn) for the Carcano and Arisaka rifles. Likewise 0.314/0.316/0.318" (weights 177/178/179 gn)for the 303 and 7.7 mm Arisaka. Worth trying befre you give up or start experimenting with expensive molds!

Patrick