I've thought of a super-earth with 30% higher gravity, a denser atmosphere, which facilitate the willing suspension of belief for my giant fireflies that terrorize the local humanoids. Due to the higher oxygen levels gunpowder firearms are a no-no, as the wrong shot can kick start a flaming inferno.
In any case, I'm a tad off track here anyway, the question is:
How would pneumatics in this world change due to the denser atmosphere?
For example, inhabitants of this pseudo-steampunk Anasazi society use a tube system to deliver letters, food, and other such material. Airguns don't necessarily outclass firearms but they don't set fire on everything so there's that.
Would the denser atmosphere hamper airguns by a considerable amount that people would default to armor bows and swords instead?
Lastly, would there be metals available in say, 15th century Europe that could withstand this increased pressure? or should I use some handwavium on that instead.
(forgive my bad grammar, and any horrifically inaccurate terms)