50
I do not change the barrels often,maybe ever 6 months, depending on how much ammo is loaded for a given caliber
the 40-72 is a Badger barrel 1-16 twist, the 38-50 is a Green Mountain Barrel in 1-12 twist
the sight setting remain the same, allowing for conditions
the 38-50 is more accurate than the 40-72....depending on conditions
I have never changed barrels at a match..but I do bring both just in case
having the same extractor is a benefit....like 32-40 and 38-55, or 30-30
I would not recommend the 40-72 aka 405 win, the case barely clears the hammer, because of the length
40-60 Maynard or 40-70SS will clear with the hammer cocked
the one i have seen chambered in 40-65, 45-70 had no problems clearing the hammer
you could get one chambered in 32-20, 25-20 with a lighter barrel and have the best of both worlds
both of my guns/barrel combinations weigh 12 pounds and 1 1/2 oz...just BPCR legal
a little heavy for the offhand for me ...but I seem to manage
hope this helps