First, I add a socket(LeftHandSocket) to weapon skeleton
Second, I update LeftHandSocket transform in ABP EventGraph, then I use LeftHandSocket world transform for two boneik node.
But its not good, left hand always jitter. Because The right hand animation affects the position of the firearm, while the EventGraph is updated before the AnimationGraph, so the LeftHandSockt always lags behind the animation.
All I need is: Evaluate Animation => Write Animation to BoneTransform => Get Current SocketTranform => IK