Stuck Round Ball

[FLINTNFIRE]

Well as the OP has pointed out the firearm has rust which is keeping the remaining part of the old lead ball stuck , speculation on what would have worked as none of us have the barrel or skin in the game , breech removal was never tried as he was worried about damaging it .

It is still an option , the question always is at what amount of force , wall hanger or will he try his idea of loading and seeing if shooting will remove what remains .

So to the original poster keep us updated on further developments .

[El Greco]

https://m.youtube.com/watch?v=jCqp9odZISg&t=1482s

[skeet1]

I would use compressed air through the nipple or remove the nipple. Make sure you point the rifle in a safe direction.

[LAGS]

I have used Mercury to disolve lead build up before on heavily leaded barrels.
I don't know if pouring mercury down the barrel will dissolve the lead balls completely , but it is worth a shot.
I used Mercury from an old thermostat mercury switch.
Those are hard to find, but I got a couple old ones from a friend that owns a A/C business .

[mooman76]

Someone from France tried dissolving a stuck ball with mercury for over a week and it did basically nothing to help.

[idahoron]

I would use compressed air through the nipple or remove the nipple. Make sure you point the rifle in a safe direction.

Compressed air would not have done anything. I know that for a fact.