Thanks revdocdrew,
Now, to keep my metric sanity, 2 3/8 is 2,375 is 60,33 mm.
IF those AA target loads really do have 70 mm hulls, well, then, 9,67 mm of extra hull would sure give some extra recoil, at least in my personal experience. More extra recoil than I got the one time I fired some true 70 mm hulled-ammo in true 65 mm chambers.
My personal standard, as appreantly is yours, is that if a few mm longer hull gives distinctly more recoil than hull same lenght as actual chamber lenght (same loads in hull), THEN that longer hull is raising the chamber pressure, which increases both muzzle velocity and recoil. MAYBE the increase in pressure still results in pressure the old gun can handle for thousands of rounds, MAYBE. I personally will stick to hull lenghts same as chamber lenghts (in the actual 65 and 67 and 70 mm chambers), or to the use of 67 mm hulls in 65 mm chambers of my old guns. I might even be willing to use lower pressure 70 mm-hulled loads in 67 mm chambers, BUT, I have done no testing in my old doubles.
Niklas
