Recently, the toxicity of lead has generated more press than its ballistic properties. A lead ban in California is said to prevent condors from eating bullet fragments in carcasses left by hunters. To serve Californians and broaden its selection of big-game bullets, Hornady has announced the GMX, a bullet without a lead core.
"GMX" stands for "gilding metal expanding." The bullet is not of solid copper, but an alloy that's 95 percent copper, 5 percent zinc. "It's the material we've used for decades in bullet jackets," says Jeremy Millard, who headed the GMX project. "This alloy doesn't foul bores as fast or as severely as pure copper."
Because gilding metal is lighter than lead, you'll find no GMX bullets pushing the high side of traditional weights for the caliber. Matching lead-bullet weights would make them too long. The GMX bullet is designed to drive deep with negligible weight loss, so light weights should be no handicap.
In tests, the GMX bullet expands and penetrates reliably at impact speeds from less than 2,000 fps to 3,400 fps. "Typically, we get 99 percent weight retention in ballistic gelatin," says Jeremy. "All we lose is the scarlet plastic tip." Yes, the GMX looks just like an SST, though the shank has two cannelures to reduce bearing surface and give displaced metal a place to go. They keep pressures in check. Inside, the two bullets differ. Besides lacking the SST's lead core, the GMX boasts a unique cavity. "The front end is parallel-sided to accept the tip," says Jeremy. "As on the SST, that's a 3⁄32-inch channel. In the GMX it tapers nearly to a point even with the base of the ogive. That's where expansion stops."
In flight, the GMX acts much like the SST. Both are of boattail design. The ballistic coefficients of same-weight bullets are almost identical.