First thing question is not for you.There are people who can understand my question perfectly.
The purpose of a forum is to have a public discussion on any subject, and posts in threads are just public statements, subject to scrutiny by any and all members.
Second i'm not talking about steel jacket,i'm talking about steel core instead of lead core.
Read it carefully..
Copper jacket over steel core.
In this context the crux of the matter is the thickness of the outermost coating. It isn't really important what is inside. It is very much possible to have either a solid metal bullet made of steel or zinc, or a jacket made of steel with lead stuffed in it. And since steel is less dense than lead, uniform solid metal bullets will weigh less than lead stuffed ones. The design decision depends on intended purpose, internal, external and terminal ballistics.
In this video is shown 5.56 Tulammo which are either copper "washed" or "plated" and uniform solid inside, also solid uniform bullet without any coating.
And USGI M80 ball 7.62x51 ammo intended for use in vietnam in the M14 rifle, manufactured in the 60s were all copper washed or plated, steel jacketed, lead stuffed/cored bullets.
So yeah it is my opinion that modern barrels with decent manufacturing methods and quality control is good for copper plated/washed ammo with whatever soft metal inside, as long as it meets your weight goal, for all practical and reasonable amount of shooting expected to be done.