Well you have to choose between what the chamberlength is called - and what is actually is. That is normally two diffrent things.
The chamberlengt was more often longer than what was stated, so 2 1/2 inch or 65mm is just something you label on the chamber. Why they started to label 2 1/2 inch when they ment 2 3/5 or even longer is odd, but that is what they used. Bottom line: a 2 1/2 inch chamber is 65mm long - or longer. There is a 63mm chamber length - but I have never seen these.
The problem is when you try to use 67mm cartridges in a true 65mm chambers. HVA normally used a chamberlength if 67mm (even if they are stamped 65mm), they stepped up to 70mm in the years before the second world war. True 65mm chambers is most often found on brittish guns, not swedish or german guns.
The swedish version is available at:
http://www.shotguns.se/html/65_and_67_5_mm_.htmlBest regards
Tobias
