When I was thinking about the pig tail I recalled the tapered curl we are familiar with in the corkscrew but perhaps not a bullet worm or a gun worm. I’ve done a fair amount of long gun shooting but never muzzleloading so I’ve never come across one first hand.
These were most commonly tapered helix devices attached to cleaning rods and were used to dislodge rifle and musket balls when a charge failed to fire. I found a few images of a some that looked like what I call an easy out. https://en.wikipedia.org/wiki/Screw_extractor
Here are some links for those who want to see more. A lot of them are American Civil War relics.