I have a jpg and a sf that are both two thirds heartwood . Both are still big bats for the weight ....perhaps they are somehow lower density heartwood ? Either way , both go like trampolines , but both got light edge cracking during knocking in /playing in process , even though i babied them them tlc . So , yeah , perhaps they are more brittle , to a degree , but they tend to play well , so long as you don't mind them not having that soft feel .