Roby, You are correct that the eagle is done by the repousse process. I did some restoration work on an original, the cheek inlay was falling off, so I removed it before reattaching it with the correct nails. The original was made of silver and was .020 thick. I have since that time made at least three copies of that rifle. I learned a valuable lesson when I carved my first form to do the repousse eagle your form will be a negative. You have to reverse the eagle to get the head pointing in the right direction. It all worked out well, since I used the first eagle to build a left hand gun...heck of a place to start building a gun a (cheekpiece inlay) I have my forms in the shop and will dig them out later today and post a few photos so you can see how I did it.
Ron