There’s two things that looks a bit off in your screenshots for this to work.
-
You have to select your wrist (or whatever bone) in the “Two Bone IK” node, currently it says “Bone: None” in your screenshot. Also, after having selected it make sure to set the effector locator space to “World Space”.
-
I think the “Joint Target Location” is actually the “pole vector location”, IE which location to “point the elbow towards”.
You usually would want to drive this location based on what animations you’re playing, but for your case now you could possibly get away with unplugging any input and just entering a component space location that’s down and off to the side a bit.
Edit:
Doing this should position the hand at your slot I think. For it all to look right you might need to also drive the orientation of the wrist joint, in case the rifle will be rotating around and stuff. Using something like a “Transform Bone” node and plugging in the orientation of the slot might do it.
Also just a note, I’m not sure why you’re doing the setup this way, but depending on your needs it might have been simpler to just attach the the weapon to the hands rather than the other way around 