Since QuasarDragon has started adding links to Project Gutenberg texts this is getting redundant, but here are a few more classic sf tales now in the public domain. Including one of the Hawk Carse stories, which were very popular back in the day, despite basically being Wild West yarns transposed into outer space. But since that seems to be all the rage amongst some people nowadays maybe they'll catch on again, although the crude racial attitudes may put some readers off. Judge for yourself.
Operation Earthworm by Joe Archibald (Fantastic Universe, September 1955)
'Septimus Spink didn't need to read Jules Verne's "Journey to the Center of the Earth." He had more amazing ideas of his own.'
The Bluff of the Hawk by Anthony Gilmore (Astounding Stories, May 1932)
'A trick? Carse was famed for them. A trap? But how?'
Pirates of the Gorm by Nathan Schachner (Astounding Stories, May 1932)
'The trail of vanished space ships leads Grant Pemberton to a marvellous lake of fire.'