The Taurus has standard rifling. H&K P7s and their brethren have polygonal rifling.
Reasons makers don't use normally it is because of expense and difficulty to do the rifling right.
Had a regular PT111 and have the PT111 Mil/pro. Been through the owner's manual and talked to Customer Service in the past. Nothing on poly. rifling. Nor is there anything about not shooting lead through the gun, anywhere.
As for the lead I have shot lead out of the pistol. Local range had some lead loads. These functioned flawlessly, but the clean up job wasn't worth all the trouble later. Fired only 20 rounds and the scrubbing,cleaning,let it soak with solvents, and all wasn't worth it.