So lately I've been toying with SpriteAnims, and have managed to sync a few assault rifles so that they have recoil/bolt animations instead of being static.

However, it doesn't seem to work with guns that don't fire full auto.

I've been using SpriteAnimMode 4, which loops the different .bmps as long as the trigger is being held, but things like sniper rifles and shotguns can't be used this way, thus it doesn't work.

Is there a SpriteAnimMode or lua workaround?

You can do some funky lua workarounds with setting the sprite number of the gun or a attachable like I did in this. Keep in mind though that the way I did it probably wasn't well done as I didn't have a lot of programming experience back then.