The best way to find out about muzzle brakes is to go online and search.
http://www.muzzlebrake.com/ is a very good site with explanations of reality. There is another site
RVB PRECISION,
http://www.rvbprecision.com/articles/10/adventures_with_muzzle_brakes?PHPSESSID=2d3287a5f657de16bab88309a6051ce1, that is also filled with good information. Holland,
http://www.hollandguns.com/, and Harrells,
http://www.harrellsprec.com/, are a couple of other sites.
I built and tried several from those links, out of steel and aluminum. One also has a program you can calculate the actual recoil reduction...you just have to check them out. Brakes all work to a greater or lessor degree and depends on many factors as to the amount of recoil reduction. A 308 would be reduced to something like a 30-30 because you still have the bullet/powder weight to contend with, but maybe that would be enough for you. Reality wise...a 50% reduction is closer to fact.
I don't have brakes on anything except my 375 H&H and 416 Taylor as recoil doesn't cause me much problem, but it does keep the muzzle down for a quicker second shot in the heavier calibers. I did try one on my 300 WM but took it off and re-crowned the barrel. I also tried one on my 22-243 Midd which again was more for keeping the muzzle down rather than recoil reduction. I might put one on the 9.3x62 I'm building...again for muzzle rise control mostly but I won't know until I get it built and see how it reacts.
Basically you are redirecting the gas jet to the sides, above or in a circle around the muzzle...this is the reduction you actually feel and what causes all the Hoo Haa with brakes because the sound is also redirected. Each has several solutions but seldom do people use one, they seem to want to whine more than anything and ear protection is the best way to solve that which should be a given even though it isn't.
I was going to put one on my NEF 45-70 BC but decided it wouldn't be de rigueur besides looking funny and having to reposition the front site.
Brakes are very simple devices, some very easy to make and others take much more work and the price range is very wide...from about 30 bucks to a couple hundred for the brake...PLUS the machining on the barrel...it is something to think about