@Antistar
How I figured it out was sorta accidental. I used the laser rifle (since it's already finished) to test the marksman carbine (simple nifskope animation tweak set as a 2 hand automatic 'attack3' animation, from 2handrifle attack4 animation) then while I was testing, I already knew the ejection port wasn't moving. Then I figured, if I copy the gun parts bones from the assault carbine animation into the renamed laser rifle animation, it might work.
So I did that, tested it and it works. I then tried it with the "This Machine" 2hrattackleft semi auto animation, copied over the shotgun ejection port bone animations, tested it with "Dinner Bell" and it works too, so I decided I'll keep Dinner Bell semi auto to make it more unique. "This Machine" was unaffected by the animation tweak because it doesn't have the necessary bones to animate the shotgun ejection port. Similar to the Sniper Rifle and Service Rifle vanilla "2haattackleft" animation, it's got both the sniper rifle gun parts bones and service rifle gun parts bones in it.
ADD:
Okay I tested it with smg loop animation. Basically, I copied over (not copy paste, more like typing in the data from one to another) gun part bones from semi automatic pistols (attackright) that's either named 'Hammer' 'Slide' 'Bar' or 'Trigger' over to the attackloop animation and tested the 9mm, 10mm, and 12.7mm shooting full auto and it works. I will update the remaining smg animations and the smg 1st person animation when I'm finished with rifles.