One of the areas of rifle collecting that is easy (and cheap) to get into and very difficult (and expensive) to master is that of Mausers. Literally dozens of countries used Mausers in scores of variations. A great many of them are still available for very affordable prices, including commonly seen Turks and Yugos and more esoteric examples such as Siamese Mausers (like this one closing today on GunBroker with no reserve and a $275 opening bid). On the other hand, the very rare examples like early Serbian 11mm carbines are scarce as hens' teeth.

Robert Ball has recently published the 5th edition of his excellent reference book on Mausers, covering all the major variants that saw service worldwide. It makes a great reference for anyone interested in Mausers or looking to expand a collection of them.