The .17 Win. Super Mag. comes with a workingman's pedigree. The case is based off a .27--caliber nail-gun blank, which was modified and necked down to take the .17-caliber bullet. (These blanks, which come in three calibers--.22, .25, and .27--are a big business for Winchester, according to Greg Kosteck, the company's marketing director.) Empty, the case measures 1.200 inches (vs. 1.064 inches for the .17 HMR). And its case walls are about 50 percent thicker than the .17 HMR's, to handle the higher pressures the round generates (33,000 psi vs. 26,000 psi for the .17 HMR).