Re: Only cracking I have done is
" but there's no point going harder than what holds the lock down."
Before the advent of cannon - stone castles were reasonably impregnable to direct attack. However - at night it was impractical to keep opening and closing the main gates. So they often had a small postern gate tucked away in the outer wall. This was the weak spot that was prone to phishing or bribery - letting a small enemy force in to open the main gate.