Getting Specific
Our sample comp is attached to a .38 Super barrel for a 1911-type pistol. It has three top ports and four side ports (two on each side). Each top port has an expansion chamber. The expansion chamber is wider than the passageway for the bullet. This is where the gas can expand and collect, as the bullet passes through. The chamber has a front wall, or baffle plate, to help redirect the gas. The side ports do not have an expansion chamber, but their front wall serves as a baffle.
When the high-speed gas hits the baffle plate, it pushes forward on the compensator. Whatever the compensator is attached to, such as the barrel, is also pushed forward. With many centerfire semi-auto pistols, the barrel and slide are locked together for the first few moments of the recoil cycle even as the slide starts to move to the rear when the bullet starts to move forward down the barrel. A 1911 operates this way. This means there is a counterforce produced by the gas hitting the compensator baffle(s), pushing the barrel/slide assembly forward to help counter their rearward movement. This slows down the slide and contributes to the reduction in felt recoil.
Slowing down the slide is not trivial in some guns. If there is sufficient forward force, the slide can be slowed down too much, and the gun won’t cycle reliably. This depends on the power of the ammunition (which mostly determines the recoil force), the amount of gas and its pressure, how many chambers (baffles) are on the compensator, the strength of the recoil spring and the weight of all the moving parts.
You might be familiar with some guns built for competition having slides with various patterns of holes cut in them. Besides looking awesome, this serves to reduce the weight of the moving parts, which can help increase reliable functioning when using a compensator.
The top ports on a compensator direct the gas upward. The upward flow of gas force is, once again thanks to Mr. Newton, countered by a downward force. This downward force reduces muzzle rise. Ta-Da.