Here I provide a partial remedy to the complaint made in Weapon jitter fix, read that before you decide whether to install this mod. My solution is simple. By restricting turning animations to lowerbody, the upperbody discrepancy between ***_idle.hkx and ***_turn***.hkx is removed. Here is how I do it. In behavior files there is a thing called BSBoneSwitchGenerator which is used to apply different animations to different body parts. Let's take 1hm_behavior as an example. Open 1hm_behavior.xml, search SneakWeap_TurnLeft_BoneSwitch. This is a preexisting BSBoneSwitchGenerator used to play different animations on upper/lower body while sneaking. You should find something like
<hkobject name="#4195" class="BSBoneSwitchGeneratorBoneData" signature="0xc1215be6">
<hkparam name="variableBindingSet">#4240</hkparam>
<hkparam name="pGenerator">#4197</hkparam>
<hkparam name="spBoneWeight">#4196</hkparam>
</hkobject>
<hkobject name="#4194" class="BSBoneSwitchGenerator" signature="0xf33d3eea">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="userData">1</hkparam>
<hkparam name="name">SneakWeap_TurnLeft_BoneSwitch</hkparam>
<hkparam name="pDefaultGenerator">#0158</hkparam>
<hkparam name="ChildrenA" numelements="1">
#4195
</hkparam>
</hkobject>.
Copy these into clipboard and search for MeleeTurnLeft_State. It's like
<hkobject name="#4243" class="hkbStateMachineStateInfo" signature="0xed7f9d0">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="listeners" numelements="0"></hkparam>
<hkparam name="enterNotifyEvents">#4245</hkparam>
<hkparam name="exitNotifyEvents">null</hkparam>
<hkparam name="transitions">#4244</hkparam>
<hkparam name="generator">#4197</hkparam>
<hkparam name="name">MeleeTurnLeft_State</hkparam>
<hkparam name="stateId">0</hkparam>
<hkparam name="probability">1.000000</hkparam>
<hkparam name="enable">true</hkparam>
</hkobject>.
Paste the content in clipboard before <hkobject name="#4243" and change their id into unused numbers, like
<hkobject name="#4892" class="BSBoneSwitchGeneratorBoneData" signature="0xc1215be6">
<hkparam name="variableBindingSet">#4240</hkparam>
<hkparam name="pGenerator">#4255</hkparam>
<hkparam name="spBoneWeight">#4196</hkparam>
</hkobject>
<hkobject name="#4893" class="BSBoneSwitchGenerator" signature="0xf33d3eea">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="userData">1</hkparam>
<hkparam name="name">Weap_TurnLeft_BoneSwitch</hkparam>
<hkparam name="pDefaultGenerator">#4197</hkparam>
<hkparam name="ChildrenA" numelements="1">
#4892
</hkparam>
</hkobject>.
I've replaced 4195 by 4892 and 4194 by 4893, which were unused identifiers. 4255 is the id of something called Weap_Idle_Behavior and 4197 is that of Weap_TurnLeft_Behavior. You need to replace these with the numbers shown in your file. Now change <hkparam name="generator">#4197 within MeleeTurnLeft_State into <hkparam name="generator">#4893 and you are done with 1&2hm_turnleft animations. Now replace Left by Right and repeat, then do similar things to mag_behavior. There are also weapon-sheathed turning animations. You can see them while controlling NPCs. I've uploaded the modified 1hm_behavior file for your convenience. If you want compatibility with other mods however, either do it youself or beg fore to include this into FNIS.
Your incarnation in skyrim will still suffer from Parkinson's if **idle and ***turn don't match well in lowerbody but this should make existing animation mods more acceptable to perfectionists.
<hkobject name="#4195" class="BSBoneSwitchGeneratorBoneData" signature="0xc1215be6">
<hkparam name="variableBindingSet">#4240</hkparam>
<hkparam name="pGenerator">#4197</hkparam>
<hkparam name="spBoneWeight">#4196</hkparam>
</hkobject>
<hkobject name="#4194" class="BSBoneSwitchGenerator" signature="0xf33d3eea">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="userData">1</hkparam>
<hkparam name="name">SneakWeap_TurnLeft_BoneSwitch</hkparam>
<hkparam name="pDefaultGenerator">#0158</hkparam>
<hkparam name="ChildrenA" numelements="1">
#4195
</hkparam>
</hkobject>.
Copy these into clipboard and search for MeleeTurnLeft_State. It's like
<hkobject name="#4243" class="hkbStateMachineStateInfo" signature="0xed7f9d0">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="listeners" numelements="0"></hkparam>
<hkparam name="enterNotifyEvents">#4245</hkparam>
<hkparam name="exitNotifyEvents">null</hkparam>
<hkparam name="transitions">#4244</hkparam>
<hkparam name="generator">#4197</hkparam>
<hkparam name="name">MeleeTurnLeft_State</hkparam>
<hkparam name="stateId">0</hkparam>
<hkparam name="probability">1.000000</hkparam>
<hkparam name="enable">true</hkparam>
</hkobject>.
Paste the content in clipboard before <hkobject name="#4243" and change their id into unused numbers, like
<hkobject name="#4892" class="BSBoneSwitchGeneratorBoneData" signature="0xc1215be6">
<hkparam name="variableBindingSet">#4240</hkparam>
<hkparam name="pGenerator">#4255</hkparam>
<hkparam name="spBoneWeight">#4196</hkparam>
</hkobject>
<hkobject name="#4893" class="BSBoneSwitchGenerator" signature="0xf33d3eea">
<hkparam name="variableBindingSet">null</hkparam>
<hkparam name="userData">1</hkparam>
<hkparam name="name">Weap_TurnLeft_BoneSwitch</hkparam>
<hkparam name="pDefaultGenerator">#4197</hkparam>
<hkparam name="ChildrenA" numelements="1">
#4892
</hkparam>
</hkobject>.
I've replaced 4195 by 4892 and 4194 by 4893, which were unused identifiers. 4255 is the id of something called Weap_Idle_Behavior and 4197 is that of Weap_TurnLeft_Behavior. You need to replace these with the numbers shown in your file. Now change <hkparam name="generator">#4197 within MeleeTurnLeft_State into <hkparam name="generator">#4893 and you are done with 1&2hm_turnleft animations. Now replace Left by Right and repeat, then do similar things to mag_behavior. There are also weapon-sheathed turning animations. You can see them while controlling NPCs. I've uploaded the modified 1hm_behavior file for your convenience. If you want compatibility with other mods however, either do it youself or beg fore to include this into FNIS.
Your incarnation in skyrim will still suffer from Parkinson's if **idle and ***turn don't match well in lowerbody but this should make existing animation mods more acceptable to perfectionists.