I did this a month or two ago. the solution I used was half ammonia, half vinegar.
Even after throughly cleaning a Mosin Nagant rifle that I have and it appearing to be totally clean, HUGE amounts of gunk came out using this method.
On the Mosin, I had used automotive brake cleaner down the barrel (and all over) to remove cosmoline. I then used bore cleaning solvent and a brass brush to scrub out the barrel. Then some CLP on a bore snake - then patches, which came out clean.
And then after using this electified cleaning of an "already clean" Mosin, here's what came out. Bear in mind the rod is smooth silver steel - anything that's not smooth steel is gunk from the barrel! I didn't photograph the junk that came out when I upended the barrel, these are just the rod and wipecloths that came out of the barrel, and a pic of the setup:
My instructions were similar to yours but used batteries:
Here's what you need:
1. some wire, maybe 3 ft
2. two or three AA batteries, you're looking for 3 volts
3. a rubber stopper (home depot has these
4. a 4' steel rod (2.38 at home depot)
5. some electrical tape
6. 2 aligator clips
8. white vinegar
10. small funnel for use at the muzzle end
Basically, rig it however you like. Stack the two batteries end to end & tape them firmly together. Or do as I did, and take the 3-AAA battery 'tray' out of a little 9LED flashlight and use it. The commercial electric cleaners use 3 volts and there may be a good reason for that, so I'd stick to 3v if you can.
Attach a wire to the positive end of the battery stack, and attach ANOTHER wire to the negative. You can tape the wires on or use any other method you like.
Attach the aligator clips to the other ends of the wires.
Plug the barrel at the chamber end with the rubber plug so that the liquid cleaner you use wont run out into the chamber area.
Wrap a few wraps of electrical tape at one end of the rod (which will sit in the chamber end after you insert the rod into the barrel from the muzzle end) and some at the end that will be just inside the muzzle. The idea is that when the rod is inserted, the rod CAN NOT touch the barrel - the tape wraps wil insulated it so there is no metal on metal contact.
Wrap some paper towel around the muzzle end so that any overflow can be absorbed. Have extra towels on hand to clean up any spills.
Make a mixture of 1 part ammonia, 1 part vinegar and 1 part water. Pour it into the barrel via the muzzle. Leave a little room at the top so it doesn't overflow when you insert the metal rod.
Insert the metal rod, wiping any overflow. Clamp an aligator clip to the steel rod that's above the muzzle (outside the barrel obviously). Clamp the other end to the metal of the barrel, any place you can find a spot.
Let it sit for an hour or so. You will see it start to foam up within about 30 seconds. Within a minute or two the white foam will turn dark brown. Once done, disconnect everything and pour the dirty liquid mixture from the barrel and wipe down the metal rod which will be really gunked up by now.
Then clean the barrel as normal with brush & CLP, etc.
This is essential for surplus rifles in my opinion.
Do at your own risk, I'm just telling about my experience but assume no responsibility for your messes, etc etc etc blah blah blah.
Be careful letting the undiluted amonia get on any gun parts or wood as I'm not sure if it could damage the finish.