5% antimony. If you use the 155 gr Lee .45 SWC mold with this alloy, the bullets drop from the mold weighing 105 grs or so. Hollowbase them to 90 grs, and with a fully supported barrel, 12.0 grs of Bullseye will get it to 2000 fps in a 4" long barreled 1911. This seems like a lot of this powder to many, but believe me, 8.0 grs of it, with this bullet, wont even cycle the slide. The pressures are not high. The bullet squirts out of the barrel before you can build much pressure. Size it .451", and the only way to size and lube such a hard bullet is with the Lee Sizer that mounts in a loading press, and Lee Liquid Lube. Zero this load at 50 yds, it's only a couple of inches low at 100 yds. It's got over 800 ft lbs and it exits the ribcage of a big Hereford bull. That's right up there, performance wise, with a 4" barreled .44 mag.