Well, thats a tough call. A lot of factors can go into how 'easy' a gun is to make.
First of all, if you already have a very good idea, or even better, profile drawings of gun you are making, it makes it much easier. Then there's level of detail blah blah blah...
I found it kind of easy. I made the 1st version of the rifle after a couple hours of tutorials... but I've also had some experience with traditional art and other 3D programs.
I would suggest downloading GMax from discreet and doing some of the tutorials. After you feel comfortable enough with the basics, try to make something and post it either here or at a low-poly modelling forum (ie polycount.com)
good luck
