GHK M4 chewing up BBs and shooting crooked
 

I recently bought a GHK M4 KM. It shoots to the left, and shreds BBs sometimes. It's got an aftermarked barrel/hop up, and I noticed that the bucking sits slightly to the left of 12 o' clock when looking down the barrel. My question is, can I go in there and realign the barrel/bucking assembly? Also, will I need a special tool? I tried to loosen off the barrel by hand but it won't budge. The collar that fastens the outer barrel to the upper receiver also has a really aggressive tooth pattern around the edge, which makes me think I need a special tool meant just for the keymod barrels. Any help is greatly appreciated!

You'll need an AR wrench to remove the barrel nut