Hello Buckstix,

I have measured (pushed a lead ball through the barrel) several rifles in this cartridge and the barrels are different.
My before World War One is in near mint condition and the barrel is 10,78mm which is 0.4244”
My before Second World War also in near mint condition is 10,75mm, which is 0.4232”

Some of my friends well used once, are running as high as 10,8mm which is 0.4252”

For those, I swage down Sierras .430” 300 grains pistol bullets to .4245” with fine accuracy. Slug your barrel and unless it is not too worn your Hawk bullets measuring .424 to .425 should be fine.

Robert