For you in-line guys, this will not be helpful at all but, if you have a side lock muzzle loader, this could be very handy, like if you put down the bullet BEFORE the powder (it happens) or even worse break your ramrod while it is in the barrel which is what prompted this project. Maybe you just want to unload quietly. Here is how you can do it.
Step 1: Get Tire Valve Stem
Go to a hardware or big box store an buy a replacement valve stem. Better yet, go to a tire shop and ask politely for a used one, they cut them off and throw them away when they install new tires so you are just asking for their garbage. The one on the left is what it looks like if you buy one, the one on the right is what you would get from the tire shop.
Step 2: Remove the Unwanted Parts
Carefully remove the rubber. A heat gun or torch may help with the final bits. The third picture is what will remain.
Step 3: What Kind of Nipple Do You Have?
Most side lock muzzle loaders have either 1/4 x 28 nf threads or metric 6x1mm threads. Obtain the appropriate die for the threads you have. Don't worry if you don't have a die handle, you won't be needing it.
Step 4: Cut the Threads
Chuck the tire valve end that would be used to put in air into the tire, into a drill press, this will ensure that the die is nice and straight. You will need a helper to hold some light pressure on the drill press handle or, if you don't have any friends, use a weight on the handle. DO NOT hit the power switch. Manually turn the drill chuck clockwise 1 turn then counterclockwise1/2 turn. Proceed clockwise one and back 1/2 until you have threads cut for about 1/2 inch (1cm)
Step 5: Install the Unloader
Remove the nipple from your gun and replace with your newly created unloader. Point in a safe direction and apply some air pressure in short bursts and the bullet and/ or stuck ram rod will pop out. 50 psi seems adequate.
Bonus!! Add some plastic tubing and this become a barrel cleaning tool when it becomes bath time for the gun. I guess in line would be easier but I just don't want to give up the old-timeyness of the side-lock. I hope you find this helpful.