Superman
If the other methods of removing what ever is stuck in the barrel doesn't work, there is another solution. It is usually reserved for the last attempts to remove an obstruction because it is rather messy.
If you don't have one, go to your auto parts store and buy a pump type grease gun. Also buy several tubes of grease. The lowest cost grease you can find that will work in the grease gun.
Also, take the removed nipple with you when you go to the auto parts store.
Show the guy the nipple and tell him you want to buy a grease fitting zerk that will match the nipple threads. (Yes, zerk.)
When you get home, screw the zerk into the nipple hole using just your fingers to screw it in. It doesn't have to be tightend with a wrench but it must turn into the hole at least 3 revolutions.
Attack the grease gun and start pumping the grease into the zerk. Keep pumping grease until the barrel obstruction is forced out of the muzzle.
After you've done this, remove the zerk leaving the nipple hole open and start removing the grease. Don't forget to clean the flame channel between the bottom of the nipple hole and the bore. A couple of pipe cleaners can help to force the grease out of that little hole.
It's a messy job but it works every time.