Two hand aiming already removes late updates which significantly stabilizes the hand jitter, i’m not entirely sure you want it slower than that without like a bipod as when turning while holding the gun it will lag behind you already. “simulate breath” shouldn’t be needed, the player can actually that for real and it will help them. Secondary grips also have a ConstantLerp value that will slow down the tracking by up to a full frame over no late updates as well which would help smooth it out.
If you REALLY want to go forward with damping the primary hand the addition transform should actually work for that, you would have to record last frames location and ones and add a reverse offset to it.