Re: muzzel brakes
MMM, let's answer your question directly. The common brake like KDF, etc reduce recoil up to 45%. Most are in the 1/3 range.
The baffle brakes, ie fishgill style, can go up to around 65%. The larger the brake diameter, and, to a point, the number of gills/ports, the more effective the brake.
I put a large port on my 300RUM. Just a 3/4" hole in the barrel. This reduced the amount my rifle moves back by 2/3. Went from moving 3" to 1". It's a real pussycat to shoot now.
The larger 50BMG style that vent backwards and have large "sails" are supposed to go up to 75%.
So much depends on the barrel length, cartridge and muzzle gas pressure. The higher the pressure and larger the gas volume, the more effective any brake design will be.
The "quieter" the brake, the less effective it is because more gas is allowed to vent forward. The BMG styles like you see on the AR50 and Barretts are very effective, BUT the noise and concussion is high.
I use muzzle brakes on all my cannons and wouldn't shoot without one. I also use the best ear plug under my 31 dB ear muffs.