Hello
As I understand it, the "Nitro" stamp on the barrel was the proof mark that Husqvarna used to designate that particular barrel as having been proof tested. I am only speaking of the HVA/1900 rifles because the 98/96 guns are a different bird. Not all the HVA or the 1900 actioned rifles have barrels that are Nitro marked. That said I haven't seen a lot that didn't say Nitro. In looking through my safe(way too many Huskies!!!) there is only one there right now that doesn't have it, and that is a 1900 in 25-06 that shoots one hole groups. Needless to say, I'm not too worried about the stamp being missing. There is more to the proof markings that I am not remembering. I highly doubt the barrels that don't have the Nitro stamp weren't proofed. I seem to remember something about the ones being marked Nitro being proof tested by a Swedish government tester or lab. The other barrels were just proofed by a Husqvarna tester I imagine????? This isn't gospel and just my ramblings. Maybe Ted has some input on this? Hope this helps guys. If you get the serial # it is pretty easy to age them.
Regards
Greg