I’ve seen this subject beat to death on here. One poster has shown how different designs in mechanical geometry do what they do. I’ve owned S&W
since early 70s and always had a turn line on any that I owned. As many Colt handguns I’ve owned in that same period I never owned a Colt SAA until like four years ago. After getting educated by how to properly handle a Colt SAA,if done correctly NO turn line. My blue CH 45 ACP has been shot hundreds of times and cycled into the thousands,no turn line! You will get a
little blue loss in the cylinder notches from where but very little. I realize in my picture the ACP cylinder is out of the gun so you can’t see the lack of a turn line but trust me it looks just like the 45 Colt cylinder that’s in the gun.
Pete