heritageguy gave you the goods, good job!
For the XD, the recoil spring is what cocks the striker, and holds the slide in battery. You can get a feel for this by making sure you pistol in not loaded (leave the magazine out and track the slide several times to check). Feel the force it takes to move the slide while cocked, then dry fire it (always keep the barrel in a safe direction even though you know it is not loaded, good habits) and feel the force it takes now that the striker is released. It is much higher with the striker fired. For the 9/.40 pistols the striker spring is around 4-4.5 lbs force, I have not checked on the .45ACP models.