While doing some research into guns, I found The Metropolitan Museum of New York, and they have a wonderful section for Longrifles, and the image resolution is incredible, not too mention the images are open source, no copyright, so that can be useful too.
But boy oh boy, what a great resource I feel for the builder.
Link below, let it load, it takes awhile, then click on the image, then click on it again, and use their zoom in and zoom out features. You can also download the images and use them for any purpose.
https://www.metmuseum.org/search-results#!/search?q=longrifleJust thought it may be helpful to some.