So, here are the problems, if you have used this tutorial and are wondering why npcs cannot fire your guns after you changed your acttables.
acttables are the activities for the npcs animations, here they use "SMG1" animations and if you have most likely copy+pasted the ar2 acttables, you need to search "Operator_HandleAnimEvent" in your custom weapon's code, find "EVENT_WEAPON_SMG1" (which is close to the top) and change it to "EVENT_WEAPON_AR2"
Another problem being you could've done was make the weapon use an inappropriate worldmodel, so in your mod change the worldmodel to the w_smg1.mdl or your custom smg1 worldmodel, if you have changed the acttables change the worldmodel to w_ar2.mdl or your custom ar2 worldmodel.
I am not a programmer, rather an animator and modeller so I am very sorry if you still experience issues.