Hello Daryl,
You mentioned that your head spacing is 0.019" longer which is 0,4826 mm, or roughly 0,5 mm - that made me thinking. Here is my weak theory. The 8x57 case is 57 mm long, the 9,3x57 mm case is only 56,5 mm long. In the early days the Husqvarna people had no drawings and they just run the reamer 0,5 mm to deep into the barrel for a 57 mm long case.

Anyhow, you could be happy that your rifle likes all bullet weight. As mine only like the heavy once, I have shortend the barrel to 20" for short range work, following wounded animals through the bush.

Robert