I'm glad you removed that stuck ball, however, IMHO, you did it the hard way.
IF I remember correctly, the GPR has a patent breech system that requires about 20-30 gr of powder to fill.
Assuming that you have a flint gun, enough powder can be picked into the powder chamber to blow the ball out without removing the vent.
In the case of a cap gun, remove the nipple and trickle enough BLACK powder into the flash channel to blow the ball out.
As someone mentioned, it takes surprisingly little powder to blow the ball out.
I mentioned trickling BLACK powder into the flash channel because the grains of most subs are too large to enter the channel.
Several years ago, I noticed a new rendezvouer trying to clear his rifle. It wouldn't fire. His friend, and who needs friends like this one, removed the nipple and tried to trickle pyrodex into the flash channel. The grains were too large to work their way down the channel, and the "friend" wrenched the nipple down onto the pyro, compressing it into a solid mass.
The gun still wouldn't fire, so the "friend" left the poor slob to fend for himself.
This poor kid looked like he was ready to cry, so I walked over to offer my help. The nipple was removed to find a mass of pyro so solid that even a good vent pick would barely penetrate the mass.
The cleanout screw was eventually removed, and the pick used to vent the solid mass of pyr out of the "cleanout".
The nipple was reinstalled and the gun fired, minus the cleanout screw. Normally, I wouldn't dare do something like this, but this was one of those rare situations calling for extreme measures. :nono:
The pyro sounded like a bottle rocket streaking for the stars, as it vented through the "cleanout". The gun fired, in what seemed like several seconds later, as the pyro finally burned through to the main charge.
The screw was installed in the cleanout, and the shooter instructed to reload to insure that the flash channel was now clear. His gun still wouldn't fire, so the nipple removed and enough priming trickled into the flash channel to fire the piece. No venting was necessary.
I made him clean the breech before He was allowed to reload. His gun fired without fail after cleaning the congealed oil from the breech.
The moral of the story is; clean the breech well and always use black powder. One never knows when the subs will cause more problems than they promise to solve.
J.D.