And finally, Option C:

A) No default attachments. Option removed.
B) The weapon contains all bonuses from the attachments internally, and transformations to change these bonuses all result from transforming the gun itself.

This is similar to option B, but here we literally remove the concept of "integral" attachments completely. In other words, the 2x Mag Factor for example will come from the gun itself - with no scope installed in the scope slot.

This option takes slightly less work for the modder, but there still need to be lots of versions of the gun, with different bonuses for each version. Again, this means the gun has a lot of transformations available (thus lots of versions) but has no problem transforming back and forth as it pleases.