.17-357

.17-357 (Handloader Issue #218)

The .17-357 is one of the more obscure and experimental wildcat cartridges in the .17 caliber family, developed by necking down a .357 Magnum case to accept a .172-inch bullet. The result is a bottlenecked pistol cartridge with unusual performance characteristics that push the boundaries of small-bore ballistics in handgun platforms. Its unique case geometry combines the large capacity of the .357 Magnum with the extremely small bore of a .17-caliber bullet, resulting in very high velocities and rapid energy transfer on impact.

This cartridge was featured in Handloader Issue #218, where the author explored its performance in both revolver and single-shot platforms. The .17-357 stands out due to its capacity for extremely flat trajectories at close to moderate ranges, making it a niche option for varmint control or simply as a handloading curiosity. While recoil remains relatively mild, the sharp muzzle report and muzzle flash reflect the high pressures generated by the necked-down magnum case.

Reloading the .17-357 presents certain challenges. Forming brass requires precision, as necking down the .357 Magnum to accept such a small projectile can lead to case neck tension and concentricity issues if not done carefully. The case also benefits from careful trimming and annealing, as work-hardening is a risk during the resizing process. Primers commonly used are small pistol or small rifle, depending on the firearm platform and load intensity.

Powder selection plays a crucial role in safely optimizing performance. Fast to medium burn rate powders like H110, Lil'Gun, and Accurate No. 9 are commonly tested in the .17-357, offering a balance of pressure and efficiency. Load data is sparse due to the cartridge’s rarity, so conservative load development is essential. Shooters are advised to begin with minimum charges and work up slowly while watching for signs of overpressure.

Due to its non-standard nature, the .17-357 is not commercially supported and remains a handloading-only endeavor. It appeals to reloaders interested in pushing the envelope of ballistic design and exploring the outer edges of cartridge innovation. While not practical for all applications, it remains a fascinating example of how traditional revolver rounds can be reimagined into something entirely unexpected.

Source: Handloader Issue #218 – August, 2002