Dirty barrel.

I have decided to try electrolysis to remove and loosen the crap. 

My local armoury gifted me a solution for the process. So I will set up a DIY rig and see how it goes. 

One point that seems odd to me; having looked at several examples of this method on the net. Most say use the "positive" on the barrel and negative on the cleaning rod. But my brain is telling me that current flow is from negative to positive, so I would expect it to be negative to barrel, positive to the rod. 

Anyone actually used this method sucessfully ?

I use it regularly on anything rusty that needs a good clean.  Most recently, I used it on a 6Lb AP projectile.  The part being cleaned will turn black (or at least a dark grey) and will rust very quickly afterwards, so will need to be oiled quickly.  I would try with a test piece to see if you are happy with the result.  to do the inside of a barrel, you will need a non-conductive stopper at each end, to ensure the anode and cathode do not touch.  If your voltage source has an ammeter on it, watch and see when the current draw drops.  Once this happens, run under hot water to flush out all the crud and scrub with a brush.  Rinse and repeat, as they say.

IIRC the electrolysis works by changing the electron sheIIs in the material to be removed, adding or subtracting one from the outer sheII depending on what material it is?

If I'm right it's quite possible its electron stripping intentionally?

Here is a trigger assembly from a MH rifle that had been converted to 303, only to have someone discard it in the desert when a she!! casing got stuck.  At some point it has been driven over and has two bends in the barrel.  I have disassembled the action and slowly running the parts through the electrolysis tank to clean them up.  The trigger isn't freed up yet but I have gotten enough rust off the block to now see the retaining screw for the firing pin.  The rifle and action body has been sectioned and I plan to section the block once I can get the firing pin out.  It should make a nice wall hanger once done.

The solution starts fizzing immediately when the current is on. It slows after 10-12 minutes. I carried out two 12 minute sessions on this piece.

This was connected Negative to the rusty pipe and Positive to the clean rod. 

The solution turned rusty brown and the pipe is definitely cleaner. 

But I will test with Sodium carbonate. 

Regarding the different polarity mentioned in the various techniques; could it be due to what we are trying to remove? Would Copper removal require the opposite polarity to rust?

I will post some pics, but can't do it from my phone ! Files are too big.

 I have not tried it yet. The Armourer also gave me a bottle of "Cop Out" and suggested the electrolysis. He showed me some bore scope images of a 30.06 that he had used this method on. 

I showed him the bore image of the Maltby. He thought it could be effective. 

This rifle was stored for around 70 years. I will continue testing the method before making a final decision.