If the .50 and larger calibers like the slow rates of twist for round ball; such as 1-60 to 1-72.
Why do the smaller calibers, such as .32 and .36, like twist rates of 1-48
for round ball?
I hadn't paid any attention to this until today, when I started shopping for a small bore rifle to use. What gives?

It's twist per calibre that's important. Try a .50 calibre 1:66" twist. 66"/.50" = 132". Try a .36 calibre 1:48" twist. 48"/.36" = 133". Pretty close. You can check out the old Greenhill twist formula which is Twist = 150 X diameter squared / Length. Since length = diameter when you're using round balls you can reduce the formula to Twist = 150 X diameter. The constant 150 is for fairly blunt bullets. It's tweaked a bit for round balls and modern streamlined bullets, but I don't have those numbers handy.

Bye
Jack

Thanks for the equation Jack. If 150 is the constant ;then it seems to be most of the common twists offered today are just a bit fast for round ball.

It's twist per calibre that's important. Try a .50 calibre 1:66" twist. 66"/.50" = 132". Try a .36 calibre 1:48" twist. 48"/.36" = 133". Pretty close. You can check out the old Greenhill twist formula which is Twist = 150 X diameter squared / Length. Since length = diameter when you're using round balls you can reduce the formula to Twist = 150 X diameter. The constant 150 is for fairly blunt bullets. It's tweaked a bit for round balls and modern streamlined bullets, but I don't have those numbers handy.

Bye
Jack

Greenhill's formula was intended for elongated projectiles used in field artillery. It is somewhat useful with BPCRs such s 45-70 etc. being only about 2" off in finding the best twist. But is pretty meaningless for PRBs.
PRB twists were well worked out before Greenhill learned math.
Dan