Hello, I have a USP 45 Tactical and i have been switching between the barrel the firearm came with (with threads) and a normal USP barrel. This is due to my having family in CA, and the threaded barrel is illegal there. I have been keeping a thread protector on the threaded barrel, but i have to remove it when switching the barrel out. When i did this several months ago I had a hard time getting the protector off, but managed it. Now I left my firearm in a safe for a few weeks and when i took it out i noticed rust in a few places and i am completely unable to remove the thread protector. I have tried WD-40 and vise-grip plyers, but all ive been doing is scraping the bluing off of it. Has anyone else had this problem? Any suggestions/advice would be appreciated.