I use to work for a company that made and installed muzzle brakes. I have fired a lot of them.

I own one gun with a muzzle break, a K-15 in .308 Norma Mag. I use it hunting. I don't wear muffs hunting.

How loud is subjective. If you are concerned about hurting your ears then it will. Take it to your local gunsmith have him cut of the 1/2" of threads and recrown the barrel and move on. But even then you should still wear hearing protection.

A proper fitting stock, particularly in a light weight gun will do wonders at felt recoil reduction. Even if all you do is cut for your length of pull and have recoil pad fit.