You're suggesting...I can deduce the weight of an object by looking at crude (2D) pictures of said object? Well, I'm just a simple country boy, so I'd want to just use a scale.
I'm just a simple country boy myself. If I know the approximate width and height of an object and I know what the object is made of then I can deduce the approximate weight of that object. The density of lead is about 11.35 g/cc. Dr. Gregory, in looking at the X-Rays of the thigh, said that the fragment in it was about 5 tenths of a millimeter by 2 millimeters. At those dimensions, the lead fragment would weigh 17.83 milligrams. One grain is equivalent to 64.8 milligrams. So, that fragment weighed about 1/4 of a grain.
After converting mm to cm:
.05 x 0.7854 x (0.2^2) = 0.0015708cc
0.0015708cc x 11.35g/cc = 0.017828
0.017828 x 1000 = 17.83 milligrams