Perhaps it'd be useful if a certain amount of XP from maxed weapons (I'm thinking 25) can be converted to (probably 1) 'free' (not weapon bound) experience that can be applied to any weapon. It'd help with the tedious grind.
This has been mentioned in a thread previously, and had many brilliant ideas come with it. http://www.shellshockliveforums.com/threads/weapon-experience-allocation.12100/