There's on of those plugs hiding in my basement somewhere! Wear your goggles!
Have never lost the plug but I was putting together my bull barrel/reverse plug Springfield Armoury 1911 once when the recoil spring slid clear of the barrel lug. The standard length guide rod went sailing into the air, hit the man cave roof and landed I knew not where.
Searched all weekend without finding it then first thing Monday morning ordered a new guide rod. It arrived, was fitted to the pistol and all sweet.
Then about 3 months later I knocked something behind the gunsafe. I pulled out all of the boxes around the sides, lay down to reach behind the safe to pick up what had fallen and yes, you guessed it, picked up the "missing" guide rod.
I now have a spare in my spare parts box.