I would think commercial hard cast wouldn't do as well in the glock barrels as jacketed.
Most are pretty hard say 17-21 bh.
A flat based bullet cast @ 10 bh would possibly be soft enough to make a good fit and seal off preventing blow by which causes the majority of leading. You would still need to check after every session for leading especially at the throat.
This has been gone through at least twice in my short time here, one time pretty extensively if you want to search threads. The results are 50/50, of corse its not recommended, but no manufacture recommends hand loads.
A very mild lapping might help prevent leading, but the glock barrels being hammered shouldn't really be in need of lapping.