Have no idea what might be causing key holing. But I can say that a 17 Cal even a 17 HMR can be a real booger to clean the carbon out of. I made the mistake of shooting a ruff count of 1200 rounds through my 17 HMR with out cleaning, accuracy had went to [beeep] in a hand basket.It took me a couple of days of scrubbing and soaking to get a patch to come out with out any black on it. what a chore, now I'll clean about every 250 rounds.If I had ,had a chamber plug so I could fill the barrel and really let it soak it would not have taken so long or would not have been so much work me thinks.