I just got some .268" bullets for my carcano, and wanted to make sure that these are ok to shoot. I drove a slug into the muzzle in, then extracted it with a rod. I measured across the widest part of the bullet (which would be the grooves in the barrel) and it came out .268. The impression on the bullet (the lands) came out at .256. Is the proper diameter bullet the one that is the groove diameter?

I would use the 6.5/.264's if you buying or making copper jackets. If your using cast I would go with something in the department of .268/.269
Although it would probably be best to ask a smithy.
Best of luck and be safe.

Yes you want a bullet as close to GROOVE dia as possible for jacketed. I shoot the Horn .268 Carcano bullets in my carcano and they are accurate bullewts. The rifle patterned like a shotgun with .264 inch bullets. For cast I shoot .272 and 270 sized bullets.

Groove diameter is the correct diameter for jacketed bullets.
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"Serious rifles have two barrels, everything else just burns gunpowder."

thanks, i was just concerned because these bullets seemed like they would be TIGHT in the bore.

(suddenly I feel retarded! and realized what I was doing wrong when I slugged my barrel!)

Oh I forgot to measure the difference in lands and groves when slugging! Oh man! that explains a lot! Wow I m out there...where is my common sense!?

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thanks, i was just concerned because these bullets seemed like they would be TIGHT in the bore.

Apparently, tight is good. To give some idea, the two-groove 303 Brit barrel is a bore diameter barrel with two narrow grooves. The fired bullet is swaged from .312 to .304. These barrels seem to be very accurate. But they don't seem to be the best for cast bullets due to insufficient driving land area resulting in a gap forming and gas leaking and flame cutting. Maybe it's just my barrel that is a bit rust damaged.

quote:

(suddenly I feel retarded! and realized what I was doing wrong when I slugged my barrel!)

There's not a man alive who has never made a mistake! A good man will admit his mistakes.