You might think about the fact that, back in the day, CORROSIVE primers were used and if the weapon was not cleaned properly, that "Frosted condition" would and did occur. I had a Mauser rifle that had that condition and just shooting and cleaning seemed to aleviate the situation. So--I sure would not rule out that situation although that may not be the case. Just file this away when looking these old guns over. Just don't be too frisky in getting hold of corrosive primers.