Heyas Papvafs. Ok sorry about that. I guess I misread your first post. Please keep in mind that I almost never play in 1st person, so I don't experience what you're talking about.
I also don't experience what you're talking about because I play with a mod called Cheat Terminal, which has a setting in it to turn off weapon sway. Which gets rid of that in all sights/scopes.
Before I mention this, please keep in mind that both iron sights AND scopes are affected by this setting. You remove it for one, you remove it for both. But the setting that controls this behavior is a setting called Stability. Which is located in the weapon's Aim Model file. Or the file that it uses if it doesn't have one of it's own.
By default most of the vanilla weapons have that setting at 1. INcreasing the value reduces the effect. So at like 10.... it's almost not there at all.
Open the Fallout4.esm file with Xedit, once the program finishes loading the files, click on the + next to fallout4.esm
Scroll down just a tad til you see an entry listed +Aim Model and click the + next to it.
Pick one. Assault Rifle is the one that I'm clicking, because it's at the top.
Now switch over to the Right side panel after it expands the file, and scroll to the very bottom of the page. Stability - Base Stability is there at almost the very bottom, if not the very bottom of the list.
If they're vanilla files, you have to extract them to another .esp as an Override in order to edit them. If they are mod weapons, you can do it right there in the mod file. But yeah, just set that 1 to higher save the changes and test. Repeat as needed.