guntech does excellent work and is on this board. Dennis Sorenson on Vanc. Island.
Bevan King will also do nice work but I think he is retired/retiring. Ron Smith in Alta. Not sure about Ted Gaillard but he is in Sask. Ellwood Epps. The list is quite long.
There are two basic styles of brakes. The first one below is sometimes called a gilled or baffled brake. I like these the best and they work very well for me. The pic is of a Micaluk brake on my 7RM. Recoil with 162gr Amax is like a 22/250. I spot my own hits.
This is a mass produce brake and very well priced. The Holland brake is similar and about three times the cost. If you have access to a drill press, making this type of brake is very easy. You just need a lathe to do the install and final boring.
The next style is also effective and very common. This one is on my 7 Mystic which also reduces recoil to zip.
The key is getting as much surface area in holes as possible. Number, location, and size doesn't matter. The one with the most metal missing wins.
If you want the highest recoil reduction, forget about front venting or forward angled holes. That reduces the overal effectiveness of any brake. The difference in noise reduction is minimal.
Actually, the BOSS is one of the loudest brakes I have used. Lowest recoil reduction too.
Jerry