Are you sure it is the spring? I just got my BK buffer and first time running it in a match I noticed the piston setup in the buffer needs to be compressed to allow BHO. The first couple times I had compressed the spring but wouldn't lock open; I was able to pull the CH just a bit more to compress the buffer piston and it locked open. For the record I'm running a PSA BCG with the weight still attached.
Also, based on my earlier readings/research, you may want to look at trying the AR-10 rifle spring on those full power loads to help with recoil.