Guys,
Copper washed soft steel is used because it is CHEAPER than a thick gilding copper jacket..... Strictly an economy measure.
Back during WWII copper here in the US was getting scarce. In an effort to preserve copper stocks the Army wanted to go to a copper washed steel jacket on our standard issue ammo for the M1. To this end, both Springfield Armory and Winchester did a thorough test to determine whether or not copper washed steel jackets would cause more barrel wear than normal gilding copper jackets.
After firing umpteen hundred thousands of rounds of ammo and taking dozens of M1 Garand barrels up to the magical "10" on the Throat Erosion scale (replacement point), their end conclusion was.....
"THERE IS NO DISCERNABLE DIFFERENCE IN BARREL WEAR BETWEEN GILDING COPPER AND COPPER WASHED STEEL JACKETS."
From that point on, most all of the US 30-06 M2 ball ammo through WWII, Korea, and Viet Nam was copper washed steel.... right to the end of production in the early 70's. I've fired quite a bit of Lake City '69 M2 ball in my Garands. It has a steel jacket..... shoots fine.
Even much of the 7.62 Nato M80 also has a steel jacket. This was the standard round for the M14......
Remember too that this experiment was done on the barrels of the WWII era.... themselves made of a somewhat softer steel than is used in today's barrel manufacture. If they can take it with no effect... then so can the rifles we shoot now.
If all you have to do is fret about whether or not a copper washed steel jacket is going to hurt your barrel, you might as well also begin wearing garlic and a crucifix around your neck and carrying large wooden stake to protect yourself from Vampires.
BTW, I've also shot a lot of the Porteuguese 7.62 in my rifles and love it. Good stuff. IIRC the much sought after Austrian Hirtenberger 7.62 is also steel jacketed.
Just my ramblings....
Garands forever,
Swampy