Thanks for the info. Lincoln Wearshield Jet-LH BU-90 looks pretty good and the price is not outrageous, about $5.00 per pound. From your experience I assume that this works well on manganese steel, that is not mentioned in Lincoln's description.
Another candidate is a rod specified for buildup of manganese steel like Wearshield 15CRMN. It's more expensive, what do you think?
My crusher is a Diamond Iron Works 916. It's not really a showpeice, I use it. I may show it at some point because it's interesting. At this point its not too easy to move around, around 4500 lb of deadweight. Your point is well taken about round hard rock, I quit doing fieldstone because it's hard on the crusher (pun intended). I threw a grapefruit-sized round piece of granite glacial fieldstone in there as a test once and it ejected it straight up at high speed and flew around my garage a while. I'm glad I didn't get hit, I bet that woulda left a mark. I mostly crush native limestone, broken concrete, and used brick mortar from demolition. The crusher is well-behaved when feeding those materials.