A LOT!!!
Seriously though, Recoil is a subjective matter. Many manufacturers and magazines have tried to quantify recoil reduction. Are they talking perceived recoil, recoil velocity, recoil energy, or some combination of all?
Believe it or not, recoil velocity and recoil energy is unchanged when adding a muzzle brake because they are both an effect of INTERNAL ballistics and, when measured scientifically, peak before the bullet reaches the muzzle, What YOU feel is Recoil MOMENTUM!!! A muzzle brake actually provides a BRAKING force to STOP the rearward momentum imparted on the rifle by the bullet and rifle pushing away from each other, and starts working as soon as the bullet exits the barrel. To cut to the chase, the amount of time the bullet spends in the barrel, the more momentum it develops.
Depending on the combination of rifle weight and cartridge, a heavier rifle with a long barrel can have more momentum, than a shorter barreled Light rifle. When you have more momentum the brake has to work harder to arrest it. You can have a slow shooting heavy gun like a .308 Sendero and a fast shooting light gun like a 300winmag Savage Axis, and the brake on the Axis will APPEAR to be more effective because the combination of light weight and higher recoil speed is easier to “Brake” and stop the recoil.
Rest Assured, when we talk effective, we MEAN effective! Don’t be fooled by others claims of Reducing Recoil by XX% because there isn’t an HONEST way of claiming an across the board reduction, That’s why you’ll see different results from different testers. ANY change in load, rifle weight, barrel length, or test method, will give different results.
In the future we will be publishing a table that will show you, by rifle and chambering, what it will FEEL like compared to a non-braked rifle as well as some test results of free recoil movement with and without brakes using certain rifles. i.e. on free recoil: level rifle on level table with locked bipod and remote trigger, Tactical 308 free recoil w/o brake 17.5″, with our standard brake or Hexmod 6″, and with our 3gun brake 7.5″, perceived felt recoil of 22wmr. or 308 Sendero w/brake will feel like a 22wmr, but a light 308 w/brake will feel like a 22lr, or 223 light varmint rifle w/brake will feel like a RedRider bb-gun(with the compass in the stock), or 300winmag Axis w/brake will feel like a heavy varmint 223, or a heavy tactical 300winmag will feel like a lightweight 223.