Demonwolf444: Yes there is at least one variant of the Jones Rotary Underlever that is sprung. I currently list an example of this, an Edmund Woods 3" wildfowler http://www.heritageguns.co.uk/Woods%20RUL%2012%20Hgun/Woods%20RUL%2012%20Hgun%20Details.htm
The spring is mounted in a recess in the back of the action and operates an 'over centre' lever that lies under the trigger plate. This lever operates on the axle of the Underlever making it positively snap in when pushed closed and takes it to the fully open position once half open.
It is P Webley's spring assisted bolting patent no. 3022 of 1866.
As Mike Rowe says, keep your fingers clear!