eagle27,
If OSR is not measurable and only visible due to a change in color, it would also mean that OSR is a storm in a teacup and of no consequence to the performance of the rifle. It would fall into the same category as normal wear on the finish or mechanism. But we do not know because no one seems able to measure OSR and it has only been seen. We are lacking much fact about OSR.

Note:

Of all the materials used in bullet manufacturing, lead is the worst conductor of heat. Brass/bronze is about three times better and pure copper is the best at about 10 times that of lead. Lead core bullets would therefore be worst at channeling heat away from the barrel wall and copper the best. There is a simple experiment to verify this fact. Measure the temperature of the chamber area of any rifle. Fire five shots at 1 minute intervals and measure the temperature 1 minute after the last shot was fired. Start with a completely cooled rifle and use different bullet types.

http://www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html