May 26, 2015
By Brad Miller, Ph.D.
Reducing pistol recoil is always welcome. Shooting is fun, but recoil's whack can be unpleasant. Many of us would be happy if nothing kicked more than a .22.
You can reduce recoil by changing the ammunition or the gun. Some ammunition manufacturers offer low-recoil versions in some calibers, but this is not yet common. If you handload your ammunition, you can use less gunpowder, different gunpowder or a different bullet weight. You can make the gun heavier, or change something that will reduce the perception of recoil, such as a recoil pad or different grips. Another option is to re-task one of the forces that contributes to recoil: gas.
When the gas produced by the burning gunpowder blasts forward from the muzzle, it produces an equal counterforce (via Newton's Third Law of Motion) to the rear, adding to the recoil force produced by the bullet's weight and velocity. Redirecting gas upwards reduces felt recoil and muzzle rise.
There are two options for redirecting gas: ports and compensators. Ports are simply holes in the barrel. Compensators are more complex. They use expansion chambers and baffle plates to trap and deflect gas. Compensators add weight and length to the gun because they attach to the end of the barrel, whereas ports don't.
Which works best? That's a tricky question because they are seldom the same size, and there are minor differences in how they use gas. The two designs likely deal with different gas pressures and volume. Ports vent gas while the bullet is still in the barrel, so gas pressure is higher coming from the ports than when it comes out the end of the barrel. On the other hand, a compensator's chambers have the potential to collect more gas volume, at least in theory. In any case, ports and compensators are different animals even though they do the same kind of work.
Port and compensator effectiveness was tested with a semiautomatic Glock Model 19C 9mm Luger pistol. The barrel has two small, elongated ports that measured 0.400" long and 0.084" wide in a "V" configuration that straddle the centerline. Their center is about 1.375" from the end of the muzzle.
Ports are usually small, so the ported barrel was tested alongside a Rowland .960 barrel with a single port compensator. The compensator's expansion chamber measured 0.385" long by 0.685" wide. The Rowland's single port is roughly 3.9 times larger than the Glock's two ports.
The Rowland compensator's bullet exit hole measured 0.468", which is a little large compared to some compensators for this caliber (9mm = 0.355 caliber). For example, compensators built for 9mm competition pistols have an exit hole nearer to 0.370". A smaller exit hole traps more gas and minimizes the amount of gas that can pass forward around the bullet. The large exit hole means that it's not as effective as it could be.
A standard non-ported Glock 19 barrel was used to compare how effectively the ported 19C barrel reduced recoil. The Rowland barrel was fired with and without the compensator.
The .960 Rowland shoots the same bullets as the 9mm Luger and is the same overall length. The difference is that the .960 has a longer case (23mm compared to 9mm Luger's 19mm) and is loaded to a higher level of performance. The test ammunition for both cartridges was loaded with the same bullet and gunpowder charge weight to the same overall length, making them more-or-less equal.
The ammunition was loaded with Remington 124-grain JHP bullets and Accurate #7 gunpowder in Starline 9mm Luger and Starline 9X23 Comp brass with Federal small pistol primers at 1.150" overall length. Two different charge weights of gunpowder were used to allow analysis with linear regression. Ten rounds were fired with each load in each barrel. Velocity was measured with a Shooting Chrony chronograph at about 10 feet.
Recoil/muzzle rise was measured with a Ransom Rest, where the distance the gun moves indicates relative recoil. The rocker arm that holds the gun pivots upward when the gun is fired, just like when it's handheld. Because the ports vent the gas upward, the reciprocal downward force reduces how far the gun pivots. Thus, the Ransom Rest is an objective method to quantitatively measure muzzle rise.
The ported Glock barrel produces less velocity than the non-ported barrel because ports bleed off some pressure while the bullet is still accelerating down the barrel. The ported barrel produced an average of 66 feet per second (fps) less velocity with the same ammunition. The Rowland barrel produced a velocity in between the two Glock barrels.
Lower velocity reduces recoil force and gun movement in the Ransom Rest. Therefore, some of the reduction in Ransom Rest movement with the ported barrel is due to the lower velocity. In order to fairly compare how effective the ports and compensator are at reducing muzzle rise, Ransom Rest movement was calculated for all four conditions (Glock ported and non-ported, Rowland with and without the compensator) when the bullet was traveling at the same velocity, which was selected as 1,100 fps.
This analysis showed that when the bullet is traveling at the same speed, the non-ported Glock barrel and the Rowland barrel without the compensator have the same Ransom Rest movement, which is what one would predict. The compensator was a little more effective than the ports at reducing muzzle rise, but they were very similar. The Glock ported barrel had 30 percent less muzzle rise, while the Rowland compensator reduced muzzle rise by 36 percent. This 6-percent difference is small—an average of only 3mm of movement after having moved 37mm (compensated Rowland barrel).
Ransom Rest movement tells only part of the story. Gun function was different with the two systems. Ammunition loaded with the small charge weight reliably cycled the gun with both Glock barrels and the Rowland barrel without the compensator. When the compensator was added, the gun suffered four cycling malfunctions of the 10 shots fired due to weaker slide movement.
The data presented here is from a second comparison. Different gunpowder was used for the first comparison, and the low charge weight load in that test failed to cycle the gun at all when the compensator was added to the Rowland barrel. The gun failed to extract and/or eject for every round. The Glock ported barrel cycled reliably with this same ammunition. Failure to fully cycle can affect Ransom Rest movement, so the ammunition was loaded with a different gunpowder and to a higher velocity to provide a stronger recoil impulse.
The difference in how the ported barrel and compensated barrel functioned with the low powered ammunition contrasts how the two systems affect recoil because the ported Glock barrel produced lower velocities than the Rowland barrel, thereby producing less recoil force, yet it still cycled. Thus, even though the Rowland barrel produced more recoil force with this ammunition, the compensator slowed down slide speed enough to cause malfunctions.
Ports and compensators differ slightly in how they reduce recoil. Ports simply vent gas upward. A compensator changes the dynamics of the recoil impulse more than just by redirecting the gas upward. When gas hits the front wall of the compensator's expansion chamber, it pushes on that wall and slows the barrel's rearward movement. Since the barrel and compensator are locked together during the early stage of the recoil phase, and the compensator adds a little weight, the result is weaker slide movement.
The Glock's ports and the Rowland's expansion chamber are not the same size, but they reduced muzzle rise by similar amounts when adjusting for differences in velocity. Each design has its tradeoffs. Ports don't add length or weight to the gun but reduce velocity, which can affect a bullet's terminal performance. Compensators reduce the felt recoil impulse by slowing slide velocity but add length and weight, which might require a weaker recoil spring to function reliably with a wide range of ammunition. That said, none of these are deal-breakers, and a significant reduction in muzzle rise is a welcome benefit.
One could imagine that these two designs compete for the same role, recoil compensation for general use or a carry gun. A single-port compensator is small enough that the gun is still concealable, and carry guns are made with this in mind, such as the Wilson Combat Carry Comp.
Companies such as Magnaport and others offer porting for nearly any gun design. Several companies (for example, EFK Fire Dragon, Bar-Sto, KKM Precision, Storm Lake, Lone Wolf) offer threaded barrels for compensators or other attachments and extended barrels with ports for some handguns. These options give shooters choices for ways to take the bite out of recoil.
More ports and expansion chambers are even more effective at reducing recoil/muzzle rise, but they also reduce bullet velocity and slide speed more, respectively. Competition pistols used in IPSC/USPSA matches with multiple compensator expansion chambers often require lightening of the slide and very light recoil springs just to get the gun to cycle reliably.
Readers considering a compensator should be aware that there are several designs, and they are not equally effective. Some require gunsmith installation and can get costly. Talk with your gunsmith about the details.
One caution is worth noting. Both ports and compensators vent gas at very high pressure. Shooters should always make sure the openings are not pointed at anyone, included themselves, when fired, or they will receive a very unpleasant—and potentially injurious—blast of flame / hot gas and gunpowder debris even at a distance of several feet.