A friend of mine, who I reload for, had an 1898 rifle with a bad spot in the chamber that's in the same place as your splits. A rough area that could have been caused by the same type of case failure, other folks over the years shooting old ammo they'd found. We rechambered it to an Ackley Improved to clean up the chamber, now I have to work on the side plate to get them to feed. I'm beginning to see that Kragicon barrel steel is somewhat soft, I recently ringed the neck area of the chamber on one of mine by using filler in a cast bullet load, and I've read a multitude of posts mentioning ringing in said barrels. Mine isn't too bad, it doesn't interfere with extraction yet. I think I'll be replacing it with a Criterion chrome moly barrel at some point in the future.