[fuzebox40]

Hey Cap, the cartridge lifter spring also lifts the hold open lever. If you remove the two break down screws and drop the stock you can see the lifter and spring function from underneeth while sliding the bolt back and forth. You'll see the spring sticks past the lifter underneeth the hold open lever, but doesn't touch the hold open lever until the lifter has no more rounds and thus rises higher also reaching and lifting the hold open lever as well.
When the hold open lever is engaged it is simply hooking the front of the bolt at the bottom right corner. You can actualy see it when it's engaged looking down through the ejector door with a flashlight.
Does it engage when you pull back the bolt manualy? If it works that way then try pulling the bolt all the way back and letting go a few times, seeing if it still works.
If it's not working anytime at all, it's either not being lifted all the way or there is wear damage at point of catch.