OK, so I figured out the relaxed rifle IK setup.
First, I had to create a large Layered Blend Per Bone node because one I didn’t want the arms to be swinging while he was walking and two I wanted the hand to be in the position of the rifle animset and not the movement animset.
So for this node, the base pose was the regular movement animset blendspace. Then I had a pin for clavicle_l, clavicle_r, lowerarm_l, and lowerarm_r. The clavicles took in a paused movement blendspace and the lowerarms took in a paused rifle blendspace.
So, the thing with UE4 IK setups is they don’t allow you to set the end effector to a socket, only to bones. I tried adding a socket to the pelvis bone and then IK the right hand bone to it, but it never worked. It only worked when I set the end effector to a bone. So for the hand_r bone, I set the effector bone to lowerarm_r and for hand_l, I set the effector to hand_r.
Since I could only use bones, I also had to add a Transform node to rotate the hand properly since I couldn’t just grab the correct rotation from the effector bone. I had to rotate both hands to be in the proper position.
This also forced me to change how my state machines transitioned, but that wasn’t a big deal and was easily solved.
Here is what my guy looks like now when equipped with a rifle:
Next comes the relaxed pistol.