A friend and I shot a lot of lead SWC bullets in IPSC competition. He was convinced that a jacketed bullet removed lead deposits from his .45 ACP. My opinion was that the jacket merely "ironed" the lead into the grooves so it appeared lead was removed.

I had an Outers Foul Out system which we used on his barrel. Lead came out in strips.

So I have the opinion that it's an old wive's tale.