Russian 5 Kopek Copper Round. Real Deal?

Certainly authentic, worth in the $10-$20 range, these large coppers are always popular

I am almost certain I read the following in a book many years ago when I was in college, but I cannot confirm this right now. Apparently there were several years of these 18th century Imperial Kopeks which seemed to be of poor quality copper (copper alloy) which was due to the fact that Imperial Russian forces recycled (ie - melted down) numerous bronze cannons which were captured during military operations. The recycled cannon metal was used to mint kopeks, and one of the reasons for the poor quality metal was the fact that the cannons weren't cleaned prior to melting resulting in a lot of impurities (think gunpowder residue). If anyone else has heard this I would love to know where they heard/read this. I was really big on Imperial Russian coinage about 15 years ago, but I have since sold most of that for US coins.