Greg Kinman (Hickok45) found that DoubleTap 10mm 230gr WFNGC hardcast lead bullets tumbled and accuracy suffered drastically fired from the G20 factory 10mm barrel with polygonal rifling. The same 230gr ammo performed well when fired from an aftermarket barrel with conventional land and groove rifling. Lighter DoubleTap 10mm 200gr WFNGC hardcast bullets performed well with the factory or aftermarket barrel. Take a look at the video with his findings at: Glock 20 with Heavy Cast Bullets (Chapter 2)
Have a model 20 gen 2 since 93 . Went into reloading due to cost & availability. I shoot lead 90% of the time, 175 gr loads at mid level charges . I do shoot 2-3 plated rounds as my final rounds ( as per Hickok) and soak barrel I solvent . I see no evidence of lead fouling.
Now if I go 200+ gr and hi charge I will ruin my brass due to the unsupported factory barrel. I have been considering a aftermarket barrel & my research thus far is that the KKM is one of the better choices. Some barrels seem to have feed issues.
I've been shooting 18-21 bhn hardness hard cast bullets through all OEM Glock barrles, in ALL the calibers of them I own, for decades now. NO issues. Use a good "hard cast." NOT, a soft lead bullet. If ya want to, check the barrel every mag full, and go on if it is NOT showing serious lead fouling, AND, it should not, IF your using good Hard Cast, and not soft lead. Works for us here, and very accurate out on our long canyon range.
I tried the AM barrels, and "for me," it was a waste of money. The OEM barrels have been super accurate enough for us, and the Hard Cast have worked fantastic all these years..