Modders have been adding weapons from Call of Duty: Modern Warfare 2 into Fallout 4, ensuring the guns feel the same down to every detail.
As well as the weapon model itself, sounds, animations, and customisability have all been ported over from MW2. The end result is a group of weapons that feel incredibly realistic in a game where weapon feel isn't a strong point.
Keeping with Fallout's lore, the military-grade weapons can be found in a locked armoury room at Fort Hagen or can be crafted with the right materials (you can also obtain it through console commands... but that's cheating).
Bethesda titles are well known for their openness for modding, with the developer releasing an official modding kit known as the Creation Kit which taps into the Creation Engine used to develop its games.
Starfield, due to be released next year, is built on the next generation of the same engine.