Well I finished the L96 specialist assignment tonight and I noticed it unlocked the final assignment 'Only for the dedicated' which unlocks the Russian Spetsnaz uniform. So its not necessary to complete all four weapon assignments if you just want the soldier camouflage. Any one will do.
If like me though you're doing them all, i'd say the quickest way is to complete one assignment fully first to open up 'Only for the dedicated', because the kills you need for the other three weapon specific assignments are counted into the final job as you're doing them.
If that makes any sense
ATTENTION EVERYBODY! Mine havent unlocked still have the little padlock thing ):
*All my spelling and grammar mistakes are on purpose.