Fred,
Let me clarify my reply above - I said that speaking only of carving & engraving. I don't take issue with obtaining proper blueprint proportions from a picture as the example you used. On that matter though, I agree with Don Getz, it's very hard to beat using the grid pattern to enlarge/shrink proportions because you can eliminate the parallax error that often accompanies a photo. If the pic was taken at any angle other than dead-perfect 90°, it won't "resize" proportionally in some areas, this is easily corrected when you do a grid copy because you'll see right away that it doesn't look right. Sorry, didn't mean to make it sound like I was saying you shouldn't get the proper dimensions of the gun.