7x57mm. The Spanish troops who made San Juan Hill hot for the Rough Riders in 1898 did so with 7x57 Mausers. One of the all-time-great game cartridges, it is a bit more powerful than the 7mm/08 but still very pleasant to shoot. It comes in a variety of bullet weights, and any one is fine for deer except the 175-grain, which is for bigger stuff. Like the 7mm/08, it works well with a 20-inch barrel.