When importing into Poser, make sure everything is unchecked on the import options dialog. If the rifle is too big, set your export options in Wings3D so that you will get proper morph targets.

I forget what Wings3D's default import/export scale is but mine is set to 20.0 for import and 0.05 for export. It sounds like you may already have these set properly, but I just wanted to make sure :)