So back on topic...
To respond to myself... highly effective for preventing corrosion/rust on raw steel, but I haven't seen much on use in bores or anything on reactivity w/ other chemicals.
I did find this informal test on AS.
Norway discontinued the use of steel core ammo due to the increased copper and zinc particulate matter causing illness. From the
paper I linked in #
141:
Compared to the lead core ammo tested, the steel core ammo produced 3x to 4x the amount of copper and zinc mg/m^3. From Section 3.2:
I doubt a monolithic copper bullet would produce the same amount of fouling as the steel core, but it would certainly be more than a lead core.