Simple vanilla ironsights
From Nexus Wiki
This is going to be very short and simple. It is meant for all the modders or anyone out there who uses NifSkope and is having trouble getting ISA onto old Fallout 3 weapons, after putting them into New Vegas.
NifSkope - you need to be slightly familiar with how to use it.
Put simply, all the vanilla weapons have that old weapons do not, are sighting nodes. These nodes tell the game where to begin aiming with ISA. Simply enough if you open a vanilla weapon in NIFSkope you'll see the little branch that says "##SightingNode" all you have to do is right click-> Copy Branch. After doing this, open whatever weapon you are trying to add ISA to, and right click the very first branch at the top, then select Block-> Paste Branch. You now notice the new branch has the wrong name, even though it adds the correct node. All you have to do is simply re-name this by clicking the "Transform" options and going to "Edit" and where it has the name box put in "##SightingNode" You have to put that exact name, otherwise it won't work. But this is a very simple way to add sighting nodes to old Fallout 3 weapons that don't have them. After re-naming the node, adjust as you see fit to hit the ironsights properly.