I have a copy of the second edition and at one time, had a copy of the first addition. The only additional information is an Appendix C which is a total of 22-pages. In these pages, there are 11-additional rifles. Great pictures of them along with information on the makers. It also includes dimensional information on the rifles. For me, I was wanting a book for reference material, not collectability which is why I sold mine and got the second addition. I guess it just boils down to what you are wanting, more info, or collectability. If you want both, keep what you have and buy the other one for reference and put the first addition back for safe keeping.
Gibster