The solution is commonly called M.A.P. (murphy's oil soap, alcohol, and hydrogen peroxide). When I make it, I mix 10% M - 45% A - 45% P. Now some will make it 20-40-40 but I just see no need for all that soap. Alcohol alone will clean a gun rather nice. In most cases, simple water with a squirt of dish soap will clean most fouling out of a barrel real well.

I also heard about the flash rust theory, but I have been told by hard core MAP users that it is false. That they clean their rifles all the time with it, and never experienced flash rust. I have used it and never experienced flash rust, but I never leave it in my rifle for any length of time either. I clean with it, wipe it out, and then oil the bore.