There is quite a bit of overlap - and the same applies to Mallory's "Krag Rifle Story".

A REAL Krag nut will ultimately have to own all three, but the last two can be somewhat expensive. If you opt for Mallory, be SURE to get the (enlarged) second edition. All three books take a slightly different approach.

And, recently, there is also a fourth, "Farmer's Notes, vol. 6" by Joe Farmer, which has GREAT data (in his own inimitable style) but sub-standard photography.

All the above are good. One place to stay away from, however, is the Bowers website - he does NOT understand the nomenclature, and thus presents very misleading data.