I am new to airguns; what is an SSG? Also the gun in question is the inexpensive, Komplete. It is regulated at 1800 psi, though I have no way to verify it. I am very happy with it and am just trying to learn different ways of tuning it for higher power. Right now I'm getting about 32 fpe with HAWKi 25.3 grn pellets, which is fine for what I intended it for, but I couldn't reconcile the shorter barrel performing better than the longer barrel gun, everything thing else being equal, almost (I don't know the regulated pressure of the short-barreled gun.). But, what you appear to be telling me is that the pressure is much greater, 2900 psi, in the unregulated gun you have, and that is how your extra energy is accomplished (?
SSG is the acronym for "Spring Stopping Guide," which is a device used to manage the energy in the hammer spring after the shot is taken. One of the things that can happen with PCPs that use mechanical knock open valves (which is most of them) is that after the shot, that valve closes quickly and the hammer gets pushed back against the spring with enough force to create a gap to the poppet, and then the hammer spring pushes the hammer back against the poppet with some force - less than a full shot, but often enough to cause the valve to open a bit and burp out a bit of air. This tendency gets worse with unregulated guns as the pressure drops in the reservoir, as the valve poppet is being held closed with decreasing force on each subsequent shot. Of course this burping results in wasted air and a louder shot than is really needed - it can get real bad as the pressure drops further, to the point that one can hear successive burps after the shot.
The SSG is a way of "capturing" the spring such that it does not occupy the full space behind the hammer, resulting in a bit of "free flight" for the hammer to have when the shot occurs. This tends to result in the hammer just bouncing off the stiff spring stack (stiffer than normal since the spring is held is slight compression by the SSG)when the valve closes, and it does not gain enough energy to knock the valve back open. Most guns don't contain these devices when new as they complicate the tuning process (more things to have to set and adjust), so they tend to be done by owners and tuners.
There are other ways of doing it, such as the SSS (Short Stiff Spring) that simply leaves space for free flight on it's own.
Here is what my SSG for the Air Ranger looks like - it has the advantage of being fully internal to the gun, so it is not seen - most SSGs result in having some part of them sticking out the rear if the gun when cocked, but I designed mine to not do that. I also attached the test results I came up with after I installed it, and you can see the gains in air efficiency that resulted, sith more gains on the back end of the shot string than on the front end (as one would expect from the physics involved in these).
One trade off that occured from adding in the SSG was that the shot to shot variation is speed increased a bit, even though the extreme spread in the sting did not - so I have a little higher standard deviation with it than without it, but the ES is the same. This makes sense, as the SSG adds another variable into the system that was not there before. The result is a little more variation in speed across the sweet spot of the tune than before, with the gains being in efficiency, shot count, and a quieter shot. There is no free lunch in any of this stuff . . .
