i never tried it with bo2 stuff so i'll rig a csgo weapon with cod4 rigs
but it'll be pretty much the same process for you, only with the same model i guess
you need to load the original model with its rigs
without binding it
then import the new model
it may be smaller or positioned differently
if so, you'll need to scale and/or rotate the model
90 degress on z axis in my case
and then scale it
and of course
try to make it the same size
and put it on the same place
it'll be a lot easier for you since both models you'll use will be the same
then delete the first model
seperate the meshes by going to mesh -> seperate
you can create layers and add the parts of the model to select them at the same time
that V thing hides the layer
select the parts of the clpi/bolt etc
and add to layer
go to display -> show -> all to unhide the hidden meshes
right click on layer -> select objects
then select the respective joint
skin -> bind skin -> smooth bind
when you're done with riggin the parts
select the whole weapon
go to edit -> select hiararchy
bind it to j_gun
that's all