Americans can order the book from Gun and Sword Collector here: https://gunandswordcollector.com/product/experiment-and-trial/
Europeans should order from Verlag Militaria here: https://www.militaria.at/Book.aspx?book=1558836&Language=en
Experiment and Trial, by Mathieu Willemsen, is a catalogue of the 218 guns in the collection of the Dutch School of Musketry, which existed from 1855 until 1933. It includes a large number of very unusual prototypes, as the School was a testing ground for designs submitted by inventors hoping to receiver Dutch military contracts. In particular, these include a wide variety of magazine conversion of the Beaumont action - designs which I have not seen any reference to anywhere else. Not everything in the book is so exotic, though, as the collection includes plenty of entirely ordinary service arms from other nations as well as from the Netherlands.
This is a fairly expensive book (€99 plus shipping in Europe; $145.50 shipped in the US), and it is definitely for a narrow group of enthusiasts. But for those of us who are particularly interested in experimental arms from the transitional period between single shot and repeating rifles, it includes quite a lot of thoroughly unique information.
Cool Forgotten Weapons merch! http://shop.bbtv.com/collections/forgotten-weapons