A police officer friend of mine got his 1911A1 Colt to go off from the half cock notch when it dropped from his back waistband while he bent over to pick up a UPS package, the bullet cut a 6-8" groove in the tile, slammed into a leather Lay-Z-Boy chair, and flopped on the carpet, while the UPS driver stood there. He truly believed the half cock was safe until then. After that, he used cocked and locked. I'm assuming a Hi Power hammer could slip from the half cock notch while getting banged, dropped, etc, and find a way to go off when you don't want it to.