Note that 65mm = 2.559" or nominally 2 9/16" (2.5625"). The British have called their guns 2½" for years, but according to both Greener & Burrard I believe except for some very early ones they have generally had chambers of from 2 9/16" to 2 5/8".

Miller/TN
I Didn't Say Everything I Said, Yogi Berra