I'm sure it works. My first thought when I heard of the method was, what a mess! If I had a rifle that had a twenty year old load in it I woudl take it apart, remove the load, inspect the barrel and reassemble. No muss no fuss. I have read on here where a shooter packed his stuff up went home and used a grease gun to remove a ball.
I agree. The grease gun method makes a real mess but it's not real hard to clean up.
If I were to rate the methods of getting a stuck ball out of a gun, this is the order I would use:
1. Use a screw type ball puller and a pinned ramrod or a steel range rod to pull the ball. (Pouring a teaspoon of water down the barrel can often loosen up a stuck patch and make pulling the ball easy.)
2. Work some loose powder down thru the flame channel after removing the nipple or thru the vent hole on a flintlock and shoot it out.
3. Get a long metal tube that just fits into the bore. Push it down until it hits the stuck ball and then pound it further down so the ball ends up inside the tube. Then, pull out the tube and ball.
4. Use a grease fitting (zerk) and a grease gun to force the stuck ball out of the barrel.
5. Unbreach the barrel and push the stuck ball out of the bore.
The reason unbreaching is last is on many guns, the breech plug is extremely tight and it's easy to damage the outside of the barrel by holding it in a vise. Some guns like CVA's and Traditions have a design that requires removing the drum or plug with the vent in it before the breech plug can be removed. Getting everything put back together on these guns, added to the very tight torque on the breech plug can be a problem.
Even on a traditional screw in type breech plug, the face of the plug must fit tightly against the shoulder at the bottom of the threads to provide a gas seal. When the plug is removed, there is usually some damage caused by its earlier installation. When the plug is reinstalled, the damaged breech plug face sometimes does not want to seal the joint without further tightening. Because the tang on the breech plug determines how the barrel is located in the stock, "overtightening" the plug is not an option because the flats of the plug and barrel flats won't line up, or the percussion drum won't be in the correct position or both.
At least that's the way I see it.