A magnet won't prove it's steel. Maybe they need to include iron in the regs.
"5. The use of any steel-jacketed or steel-core ammunition of any caliber.""
I just stuck 3 rounds of 9mm Swiss-made RUAG/Geco ammo to a magnet on the refrigerator. The bullets are stuck to the magnet, not the cases. It has a bimetal jacket - iron covered with copper.
Somebody actually ran a lab test on the stuff:
"Results
Jacket wt.-18.32grains
Core wt.-105.422grains
Jacket
4.83% Cu (plating)
94.6% Fe
.63% traces of Zn, Pb, Bi, Ni, Cr, Al
Core
98.65% Pb
1.3% Cu
<.05% Al, Fe, Bi, Zn
Samples run on ICP-OES in aqueous acid solution (digestion), 10% Aqua Regia by volume.
Yes, 95% Iron jacket (not steel) with a 5% copper plating. Core is lead."