I get railcraft enchantments like most of the time when i enchant books

It'd be better to add a config to adjust the weight of the enchantments.

There are weights?

Lol, it's the second parameter of the Enchantment constructor. In 1.9 it's an enum

• 10 -> common
• 5 -> uncommon
• 2 -> rare
• 1 -> very rare