KY Jon,
In Europe, 67 1/2mm shells are(were)sold as being safe in 65mm chambers.
Mike
True most of the time. The exceptions tend to be older 2 1/2" guns with very short and sharply tapered forcing cones. On those, you will probably know right away that the slightly longer hulls are a bad idea. Blown ends on the cases, excessive recoil. But you'll find that advice printed right on British shotshell boxes. However, it also refers to guns proofed under the old "tons" system. And if one of those older 2 1/2" guns--we're mostly talking 19th century--was reproofed back in the "tons" era (or later), then it probably also had its chambers lengthened at the same time.
