As tyler said what is it your after. I've done several varmint barrels with the customers wanting to try to maintain target aquisition better. I use two style of brakes both of which will increase the length 2" but one is better on small calibers especially if your shooting prone as there are only side ports to eliminate a dust signature.

I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them. John Wayne-The Shootist