I got this from the M2HB.net web site. http://home.flash.net/~gila/rivet_spec/rivet_a.htm You can also go to that site and they have a page on the main page that will link you directly to a section on riveting.
One suggestion is to find the right sized rivet set. I think the head size is double the shank size (1/8" rivet has a 1/4" mushroom head). Some have also heated the rivet with a propane torch first (red hot) and then used the set to form the head. It is also wise to practice with the right sized rivets on steel the correct thickness.
Now, while over on M2HB, DON'T go looking at the guns!!! You need that money for ammo! And be sure not to look at any CWA guns, as your bank book will shrivel up and die.
You need that money for ammo! 
And be sure not to look at any CWA guns, as your bank book will shrivel up and die. 
