Cobbhead,

In the one case where I did use 70 mm hulled, American-loaded shotshells in old gun with 65 mm chambers and cm-long forcing cones (I was lied to by person I bought gun from, and did not check chamber lenght) I got frayed ends of hulls and worse patterns and much greater recoil. I then cut hulls to 65 mm and used hartin crimps, which resulted in much tighter patterns and much less recoil.

In contrast, I have gotten slightly better (tighter, more even distribution) patterns when the tappered end of plastic hull extended about one half way into short (cm-length) forcing cones. Probably same effect as found by USA ammo companies in 1920-1940s with card and fiber wads. The ends of these hulls did not fray, like the ends of 70 mm hulls in 65 mm chambers. Would presume that the 50% protrusion of hull into short forcing cone simply reduces the extent of the discontinuity that shot and wads must traverse.

Niklas