.357 SIG

SIGARMS and Federal Premium Ammunition introduced the .357 SIG in 1994 to put .357 Magnum-class velocity into a semi-automatic pistol, at a time when police agencies switching from revolvers wanted the ballistic reputation of the Magnum without giving up double-stack capacity. It is a 10mm Auto case necked down to take a 9mm bullet rather than a new case built from scratch, which is why it drops into a 10mm- or .40 S&W-sized pistol with a barrel and, on some designs, a recoil spring change and nothing else.

The bottleneck is unusually pronounced for a pistol round: a 21.97 mm case narrows sharply to a 9.68 mm neck holding a 9.03 mm bullet, and that shoulder is what lets the round headspace, rather than the case mouth the way most straight-walled pistol cartridges do. C.I.P. rates it to 305 MPa; SAAMI’s 40,000 psi figure, measured by its own transducer method, is not the same number.

Both loads recorded here are drawn from the same encyclopedia ballistics table but individually footnoted to a stated test barrel, which is why they are recorded as full points rather than mass only: a 125-grain DoubleTap FMJ-FP out of a 4.5-inch barrel, and a 100-grain Cor-Bon Pow’RBall out of a 4-inch barrel — both handgun-length barrels, consistent with the round’s exclusively semi-automatic-pistol chambering.

Gaps on this page: three further rows in the same table (a Federal FMJ load, a Grizzly JHP and an Underwood TMJ) publish a velocity but no barrel length at all, so they are not recorded — an “unknown barrel” footnote in the source is treated the same as no footnote. No ballistic coefficient is published for either recorded load. Neither DVIDS nor Smithsonian Open Access returned a result for this cartridge; it saw police and civilian use rather than US military issue.