Hitting a metal pole with a small metal gate, at the bottom of a stone-wall lined 10 story stairwell. The first hit wavers a bit more, while the second hit carries more conviction.
For the play "censored on final approach" i needed the sound of artillery hitting an airplane, as heard by the pilot. I used a hammer and shovel between two closely parked cars in my grarage. Recorded using a zoom h2n.