Tbb, new bucking, SCS, and fill all air leaks and you have a system that can reach out.
Not to be a ass, but could the problem here be the user? And the way you use/aim the gun?
Not being able to hit in CQB doesn't sound like a gun issue, as even mpegs can reach out accurately to at least 20 feet.
Adjust your hop, make adjustments to your shooting strategy, and unless you have some massive air leaks or hop-up issues, it should fix your accuracy problem.