silo.
there is a 30 day free trial. making basic stuff is quite easy in silo, and as you learn the tools you can add more and more advanced parts.
guns can be easy because there are a lot of simple cylindrical and flat shapes on them - just gets more difficult if you want to add more detail and accuracy.

if you look for sob-d or box modeling tutorials, they can be applied to pretty much any modeling program. silo has an easily laid out toolset and no superfluous functions that will confuse you - just the tools you use to model.
there are also many silo specific tutorials in the silo forums.
nevercenter.com

cheers,
-gabriel