Every time I revamp/reinstall my mods I get this strange animation glitch, where people with automatic rifles shoot vertically upward when they fire instead of forward. I don't know how I fix it (sometimes I do), but does anyone else experience this?

Please post a list of active mods. In FOMM use Load Order -> Copy to clipboard and paste into a post.

Do you have RH_ironsights and Fallout Reanimated? Try reinstalling Fallout Reanimated.

I have Fallout Reanimated and get that very occasionally. They don't shoot at the sky, just aim. It doesn't happen very often to be an annoyance for me, though.

That's exactly it--pinpointed the problem. So reinstalling Fallout 3 Reanimated will fix this? Will it over-write the iron sights? I guess we'll find out...

Aha so you do have those mods. Yup its ok to overwrite the ironsight animations with fallout reanimated. in fact it is a known problem and the author "RougeHallow" recommends reinstalling fallout reanimated to fix the conflict. great mods indeed, and you might try installing FPATH it works great with reanimated and works with RH_ironsight fose too.