If I am making something like that, Ill just lay the gun on the leather, make some marks on where the gun will go, and go piece by piece. This espcially if I'm not sure what I want, or if the gun is shaped a little strange... Just keep going till it works for me. When it comes to forming, I use wood blcks and a wood mallet, put the blocks where I want a corner, or curve, put another block on top, hit it with the mallet, and form a seam that way. I do all of my forming, and then finish off with mink oil. Do the oil afterwards, because the forming of the leather with make stretched spots that will be of a lighter color.