The Eddystone rifles are known for receiver hardness but, to the best of my knowledge, the rifles with cracks in their receivers were all M1917s that had been arsenal repaired with new barrels during WWII. Apparently the original barrels were very tightly fitted. I do not know if the square threading contributed to that issue BUT I would imagine that a typical gunsmith who was not working on piece rates would take due care and warm up the receiver with a blow torch before spinnng it off such a tightly fitted barrel.
A magnaflux test would be a sensible precaution. Good luck with your project.
By the way, the first gun writer to build a .338 Lapua hunting rifle was Graham Henry, who unfortunately passed away from cancer in 2002. A subsequent editor of Barnes cartridges has removed that story from the book, in an apparent fit of xenophobia, but history is history. Graham was a great guy, and also that rarity, an honest gun writer, a local equivalent to Sam Fadala but far less prolific. I remember reading the story in New Zealand Rod & Rifle, including his account of goat hunting at what would normally be silly ranges with that rifle. Graham was an NZNRA shooter, competing at 500 to 1,000 yards, typically at Seddon Range so, for him, such long range shooting at animals was responsible.
