How do I build just a single core module?

Hi guys, sorry for the probie questions, just trying to see if I can resolve a bug.

I'd like to be able to build masterfs alone, which I can, but then when I run ant tryme the prior version is still picked up, is there a step I can take to induce the build into the set?

The module can't be reloaded in the running IDE (yeah, probie here, I stupidly tried), as it's a core module.