Id bullet shell

Went metal detecting and found what I thought was a .22, however upon comparing it appears to be slightly thicker and taller than a .22. In the picture below I have placed it next to a standard 22 for comparison.
It’s measurements are 8mm by 17mm and the headstamp is “H”
Any information is appreciated, cheers Hamish

Looks like a .30 long rimfire to me?
Even a metal detector should have basic reference books to identify his finds.