If ever needed, I have used a small air powered jack hammer under water while dredging. Used it on a lava flow over the current stream course to get to the older gravels and the real bedrock underneath.
I have also used it in large rock impacted crevices and cracks, killer on that too. Requires justification and a big heavy compressor.
Heard you can crack large boulders with it, into smaller winchable size pieces. Although never tried that.
Sliding hammers are a geat tool for the old miners tool box but very limiting and hopefully not all you bring as situations change and sometimes call for an array of sorts.