Question on Case Corrosion in “Short Term” Storage
While sorting some recently tumbled brass tonight, I found something interesting. I was sorting through some partially used boxes of reloads, trying to get spent cases back with their mates and found several rounds that appear to have a rust like corrosion on them. The copper jackets on a few of these show dark black spots near the crimp ring. Worst case on the left - moving to only slight spots to the right. All damage lower than the storage depth of the Styrofoam holder noted below.
These cases were loaded with the following components in December 2008. 38 Spl, 125g Rem SJFP, 4.8g Universal, CCI 500, in PMC cases, third loading.
Six rounds from this box were shot in mid 2009 and the box was returned to storage and stayed there until recently as I moved residences a twice and have been primarily shooting 38 HBWC and focusing on loading 45 acp since that time. Theses rounds were stored in Styrofoam blocks cased in white cardboard boxes inside an ammo can with a silica gel blocks that were oven baked twice during the 4 years. Cans were stored in cool dry room.
After finding this, I pulled remaining 6 boxes of 38 spl loaded at the same time and found no other issues. Most of the other cases actually appeared to be slightly brighter. Upon further inspection I found a small stain on the suspect box. Nothing concerning on the Styrofoam insert.
I can only surmise that one of two things happened: 1) water got on the box at the range back in 2009, or 2) the subject box must have sat on my work bench during the gun cleaning chores that day back in 2009 and received a few drops of #9 cleaner. I seriously doubt water would cause this, but wonder if the cleaner could cause such corrosion.
Anyone have input on possible causes?