You might be able to just clean up the throat depending upon how bad that erosion is. A bit more freebore.
I have had that problem with a few rifles and I moved to the heaviest/longest slug that would stabilize. In a few of those cases it worked. A far less expensive/invasive approach.
If you do move to the Whelen, check the position of the shoulder on the 9mm first, it may leave a bump. Worst case, you have to turn the barrel back a thread to give you enough new metal to work with. Then again, if you can find someone with 9mm reamer, you can do the same thing and keep the chambering intact.
Tom
