The .40 S&W and 10mm Auto share the same 0.400" groove diameter but deliver very different pressure levels - and this .40 caliber brass jag cleans both. The jag's solid brass body threads onto a standard cleaning rod and pushes patches through the bore under firm, even pressure. That tight patch-to-bore contact is what makes a gun cleaning jag more effective than a slotted tip for stripping fouling from a pistol barrel.
The .40 S&W became the dominant law enforcement cartridge for two decades, and millions of service pistols still chamber it. The 10mm Auto is its full-power parent - popular with handgun hunters and woods carry. Both cartridges produce moderate copper fouling from jacketed hollow points and noticeable carbon buildup around the throat. For duty or carry guns that cycle hundreds of rounds between cleanings, that fouling can eventually affect feeding reliability if it migrates into the chamber.
Clean your .40 cal bore after every range trip: wet patch on the brass jag, let the solvent work, brush, then dry patches on the jag until clean. This bore cleaning routine takes five minutes and keeps the pistol running. The brass material won't react with standard gun cleaning solvents, though ammonia-based copper removers may leave a blue tint on patches - that's the brass, not your barrel.
