What are the exact effects of firing a weapon if you don't meet the strength and skill requirements?

Each weapon has a strength requirement and a skill requirement, but you can still fire them anyway. As an example the Anti-Materiel Rifle needs 100 Guns skill and a strength of 8 to use.

I've read that a weapon is less effective if you don't meet the requirements, but what are the exact effects? Is the damage reduced, or the accuracy or something else entirely?

Solution 1:

In the case of Guns, not meeting the Strength requirement manifests itself as a significantly increased spread on your shots - in other words, Accuracy is substantially reduced, especially at longer ranges. Similarly, when attempting to aim the weapon using Iron Sights, Scopes, or Zoom, you'll notice substantially more 'wobble' in the camera as you struggle to manage the weight of the gun. The latter effect also manifests when attempting to use guns for which you lack the appropriate skill level. Furthermore, Damage is reduced.

For Melee weapons, Str requirements that aren't met affect attack speed, while skill requirements affect damage output, and access to 'special attacks' in VATS that do additional damage, or have additional effects.