Be sure about this one
Hi 416, I swapped off my Vanguard which is a Howa. In the fine print, they noted a barrel thread pitch, of 1.5mm. I believe this works out to slightly quicker than 20 TPI. What I would watch out for is someone trying to barrel without the correct metric transposing gear train in their lathe. If you crab the barrel threads into the receiver, then you re-create the old 7.7 Arisaka's problems with blowing barrels out of receivers, when gunsmiths tried to use 12TPI. My Logan 11 inch lathe does have the 11TPI in it's Quick Change gear box. It was made in 1947, about fifty beds before Logan changed everything in that year. I'm sure Weatherby has everything needed to rebarrel Vanguards, but I'm doubting that everyone who tries this, does. I know it's hard to believe just how springy, steel can be when put under extreme pressures. But your proposed cartridges aren't a good place to experiment with. Strangely, the older Arisakas in 6.5mm, used a 14TPI which is pretty easy to do on U.S. equipment. I'm wondering how long it will be before some "PUFF" gunwriter mentions the barrel thread pattern in the new imported Win. M 94's. FWIW, your Howa's 1.5mm threads would be very close to the old Winnie's 20TPI.