The slide locks default/rest position is down...pulled down by a spring. If there is an empty mag, the mag holds the slide lock up...or with no mag you hold the slide lock up manually. Other than that the slide lock is pulled down by the spring (without the spring, I would think by gravity) and the slide goes forward.
I can't see it working any other way, or your slide would lock back after every shot.
Actually, there is a leaf spring that holds the slide stop down.
Because of spring pressure in the mag, the mag
follower rises after the last round is loaded, and a tab on the follower engages the slide stop, pushing it up and overcoming its spring.
Before firing, with the slide in battery and an empty mag in the gun, the slide stop is pressing up against the left bottom edge of the slide.
When the slide retracts, either by firing or manually pulling it back, the slide stop snaps up into the notch in the bottom of the slide and is held up by mag spring pressure. When the slide comes far enough forward under recoil spring pressure, the stop will engage the back of the notch. Now
recoil spring pressure holds the slide against the stop.
If the empty mag stays in the gun, the spring pushing up on the slide stop
plus the friction caused by the slide recoil spring makes the slide stop hard to press down with a finger.
Remove the mag and the mag spring pressure holding the stop up goes away. Then only the recoil spring pressure has to be overcome to drop the slide stop, but that can be a lot of friction.
With the slide locked back by the stop and the mag removed, if the slide is retracted by any manual method, the friction goes away, the slide stop spring pushes the stop down, and the slide should go forward into battery.
If you try to slingshot the slide to release it when an empty mag is in the gun, the follower is pushing up against the slide stop and it will not drop.
When a loaded mag is in the gun with the slide locked back, the mag follower is not pushing up against the slide stop. Manually retracting the slide will allow the stop to drop under its own spring pressure so the slide can go forward under recoil spring pressure.
With the slide locked back you could also use a finger (usually the thumb) to push the slide stop down when the mag well is empty or there is a loaded mag in there. This can still be difficult depending on how much friction there is between the stop and the slide. This friction can be reduced with some sandpaper.
That's what I understand to be the normal functioning of a slide stop. If the OP tries to manually release the slide lock (slingshot) without a mag in the gun and it won't go into battery, that's a problem. If it won't do it with a loaded mag, that's a problem.
Does the slide stop drop down properly and then the slide not go forward? That would be a slide/recoil spring/barrel problem. But if the slide stop is not dropping down when it should, then you have a slide stop problem.
