Just to say that all cocking knobs were not fitted with the barrel insert a lot of them are just plane wood with the hole drilled in the back. Those that do have a insert can be of brass and also of a plastic material .If fitted they do not normally drop out i would have thought.The box you have there is a delux one and would have a tin of 100 pellets in the other hole in the case. It would be nice to see pics of lid of the case.