i mis-wrote octagonal, obviously it's polygonal. Anyway, Glock advises against shooting bare cast lead bullets in their stock barrels. The rifling is prone to increased leading from bare bullets. There's also the issue of the abrupt change from chamber to rifling in Glock barrels, another place, and a particularly not nice place, for excess lead buildup.
There is a brisk business in selling change-out barrels for Glocks to allow reloaders to safely shoot cast lead through them. I have a friend who thinks this is nonsense and shoots hot .40 reloads in his stock Glock. The number of alarmingly bulged cases that thing throws out gives me the willies.

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