Steve, yes it's perfectly safe. Glock recommends against shooting unjacketed/lead bullets because of the polygonal rifling in their barrels but as long as you clean the barrel regularly you'll be fine. There's plenty of reviews on people shooting heavy hard cast lead loads in their Glock 20sf. Id recommend if you plan on shooting alot of hard cast lead threw it to purchase a aftermarket barrel with standard rifling. If you only plan on using them once in awhile the factory Barrel will do just fine with proper cleaning. Hope this helps.

Hi Steve, yes you can in moderation if you use Hard Cast Lead. I use Underwood and Doubletap 200gr Lead Loads for years without any issues. Just check for leading and clean your barrel when needed when using any lead loads and you will be perfectly fine. Cheers and stay safe!