I think I found the manufacturer of your rifle. It is an Italian company named " Armi-sport." Here is a link to their website:

www.armisport.com

They list their Kentucky long rifle on the product page as having a 1-in-48" twist, which makes it best suited to patched roundballs and lighter conicals. Since it' s a currently manufactured rifle it should be good for up to at least 90grains of FFg black powder or equivalent.

Looks like a nice reproduction gun.

Mike