I know I'm reviving an old thread, but the orange stuff you speak of has showed up in quite a few Mosin's and most often it's behind the buttplate. No one really knows what it is. Some people believe its old dried up cosmoline, others believe it's an adhesive and yes, there is even a theory out there about it being cyanide and it was placed in other spots on the rifle that the Russians were suppose to lick in order to avoid being captured...... :roll:
The simple answer is, there is no answer. Just an interesting tale as to what it could be.
GB