Since you specifically mentioned guns and weapons, here's a few further thoughts:
If you saw the Sound Gun video on sound design, the most basic rule to getting effective, powerful sounds is to use layering. Even high-quality assets (like stuff from Boom Library) won't always work great on their own (and professional material from places like Boom will be pre-made out of a lot of layers to begin with). You're looking for elements you can combine together to create the sounds you want (consider pitch, texture, and other qualities), similar to how you'd do for visual effects - tackling a problem in pieces is a lot easier than looking for one singular solution.
Here's a video regarding the gun layering I did for VGHS, linked here.
And here's a second video more broadly including some free tips and software suggestions for sound design.
Sound libraries is definitely something crucial to address at RJFS, and it's something I'm looking to address, as well as providing some downloadable assets as we move forward.