Long overdue update: I found a much faster way that also makes sure the gun looks the way it should look while in ADS

Port all the non-ADS anims without changing any positions. Then you can open the the ADS up and down anims and on the frames where the gun will be in its regular idle state (last frame of ADS down and first frame of ADS up), you do the following. Select the tag_ads joint if it's on IW viewhands or tag_torso if it's on 3arc viewhands. Make a group containing that joint, and then keyframe the first frame and the last frame. For ADS up anims, you put the following translations on the first row for the group in the first frame: "-4.600" "1.200" "0.500". For ADS down anims, do the same thing except on the last frame. Make sure the other keyframe on both of these anims have the translation of the group set as "0.000 0.000 0.000" so that it looks normal while aiming.

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