How to use Kanji for naming stuff?

So basically, I want to create some japanese names for some significant weapons in a story I'm creating but I don't know how to name them, or rather what kanji to use. Mostly my idea was to just put two kanji together to form the name, but that's where the problem comes. For example I have a spear and I want it to have the kanji for "pierce". This is one of the kanji I found.
https://jisho.org/search/%E6%92%9E%20%23kanji
However, only the kun-reading actually relates to piercing while the on-readings are very different but afaik, when putting two kanji together you always use the on-readings. So how do I do this?
Can I still use the on-reading without changing it's meaning?
Is it possible to use the kun-reading despite it being two kanji together?
Do I just find another kanji entirely, and if so, how do I easily find a kanji that follows all these rules?