Unprincipled snapper on the case of your independent manuscripts (6)
I believe the answer is:
papyri
'manuscripts' is the definition.
(I've seen this before)
'unprincipled snapper on the case of your independent' is the wordplay.
'unprincipled snapper' becomes 'pap' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'the case of' means to remove the middle letters (outsides of).
'independent' becomes 'i'.
'your' with its middle taken out is 'yr'.
'pap'+'yr'+'i'='PAPYRI'
Can you help me to learn more?
(Other definitions for papyri that I've seen before include "writing stuff" , "writer's out-of-date material" , "Old manuscripts" , "Documents of old" .)