What evidence supports the claim that a dual recoil spring reduces recoil?
The claims that a dual recoil spring (DRS) reduces recoil (compared to a single spring) seem to come from gun magazines and subjective impressions. Then these unsupported claims get parroted until they are assumed to be factual. Have there been any blind tests that concludes anything or have there been any tests at all?
From an engineering perspective, this claim is questionable. The simple purpose of the recoil spring is to decelerate the slide to a stop and then return it to the closed position. Since the energy imparted to the slide is fixed, i.e. controlled by the mass and energy of the bullet, AND the distance the slide has to stop in without dead-ending on the frame is also fixed, a DRS has to absorb the very same energy, motion, and velocity in the very same distance as a single spring does.
The only thing a DRS can do is change the velocity profile of the slide. E.g. a DRS can have a weaker spring weight to start with (as in the GLock gen 4 DRS) but then somewhere along the slide travel rearward, the spring rate has to increase to a much higher rate so that the average force of the spring over the distance the slide travels is essentially the same as a single spring.
Now, it's clear to me that this may provide a desirable operational or functional characteristic, like letting the slide open a bit quicker, but in no way does it suggest that a DRS either increases or decreases recoil. For a given load, the recoil energy is constant and dependent on the mass and energy of the bullet. Either the single spring or a DRS has to absorb that energy.
The recoil profile will be modified, but again, the math doesn't support whether the changed profile will feel like more or less recoil.
So why do we keep hearing a dual recoil spring reduces the felt recoil? If it really did, doesn't it seem odd that the majority of manufacturers use single recoil springs?