Im with BP-TEC and we understand brakes, at least we think we do.
You can read the dynamics of rifle recoil at http://www.bp-tec.com/recoil.htm
How are VA Comp is different
Our brake uses the residual pressure and actually slows down the gasses. We work in 2 planes, horizontal and vertical.
Our exit bore in all 4 baffles is usually greater than .500. How can this work, because we actually designed this with a modelling program that is used for high pressure fluids. We could actually model it in time, pressure and volume. Each chamber has the same pressure.The gas velocity from each of the 4 venturies is the same volume and pressure, over the same time frame.
We tune the brake by increasing the internal bore, bleeding off excess gas. There is in most modern rifles more gas than we can use, the side effect to this is no increase in noise as the presure wave is slowed down and sound is a function of pressure. We spread this decreased pressure over a longer period of time through the 4 chambers. The pressure wave is spread over a longer time frame, the length of the VA Comp 1.75 inches.
The function of pressure that we work with is determined more by case and barrel volume than anything else.
Since we shape the high pressure gas, we are actually slowing it down. In most cases we are at 0 db over no muzzle device, sometimes as much as -1dba.
We have done near and far field sound pressure tests with M4, M16 and .308 Bolt guns.
In the videos if you watch the shooters head after the shot in the before and after in slow motion, the reduced head movement is the major factor. By making the rifle hold its horizontal plane, the body is not twisted upward by muzzle rise and much less head movement. We also decelerate the rifle with the 4 baffles at a much slower rate. Thus a much softer feel with no muzzle rise and the rifle is much softer feeling.
Actual reduction in recoil with 7 to 8 lb rifles is around 35% and 40 to 45% for rifles in the 8.5 to 10lb category.
The site is www.bp-tec.com