Recently, Istvan Peli, lead artist for the Fallout series, revealed one of the secrets of the game's production during a conversation with EDGE. As it turned out, Bethesda used a weapon scaling trick so that it wouldn't look ridiculous in the hands of a character clad in power armor.
In Fallout 4, the armor increased in size, began to resemble a mech (combat robot), and ordinary weapons looked too small because of its size:
We wanted something big, massive, that fit the atmosphere. However, in the balancing process, it turned into an ordinary assault rifle. In the hands of an ordinary person, such a weapon looks really ridiculous, too big, but we put up with it.
The visual scaling trick was also used for the player's equipment:
When you're in power armor and holding a regular weapon, we slightly scale [increase it in size]. There's a slight distortion there — you may not notice it when playing in third person, so the weapon doesn't look ridiculous. We resorted to a little trick to compensate for the strange shift and slight mismatch in scale.
Fallout has its own separate universe, the developers did not strive for realism and therefore could present a variety of models:
The cars are ridiculous, huge, massive barges with small nuclear reactors in the back. Everything is a little bloated, a little exaggerated compared to normal.