Here's what I find for the Husky guns.

All Husqvarna Hammer guns are made with 65mm chambers.
The Husqvarna Drilling, Model 70, has 65mm chambers.

All Husqvarna Hammerless guns serial numbered before 165900 are 65mm. Higher serial numbers are always 70mm. Husqvarna never made 75mm chambers.
Exceptions are:

* Model 355 Extra Lyx which was always 65mm.
* Model 310X and 310XN which were always 70mm.
* Special orders. These are usually marked with chamber length on rib or by extractors.