Ammonia's not king anymore. Over the last decade a couple of new chemistries have appeared that act faster and more completely. Probably the best one is KG-12. Jim Owens has pictures up.
Take a look at how much copper it eats off. 9.5 grains off a bullet in the same time that teh ammonia in Sweet's takes off 0.02 grains in the same conditions. The only drawback is it doesn't turn blue or green, so you have to follow it with something that does if you want proof the copper is gone.
KG-12 is what I hit heavy copper fouling with, but for normal cleaning I use Bore Tech Eliminator. It doesn't have the copper capacity of KG-12, but it's way faster than ammonia. You can't use a brass jag or bronze brush with it without everything immediately turning blue. They make a special alloy jag you can buy that isn't attacked by it, or just use a Hoppe's plastic jag. It loosens carbon really well and even etches cast bullet alloy (though very gradually). On top of all that, Eliminator is water based (so it removes corrosive priming residue easily), odorless, and non-toxic. It has corrosion inhibitors so it may be left in a bore indefinitely.
These days I keep a little pump sprayer of Eliminator in my range box. At the end of the range session I tip the muzzle down and squirt a pump or two into the chamber and let it run down the bore to the muzzle. I stick a rag in the breech to protect the bedding from any excess, and a Neoprene stopper in the muzzle to protect rifle case, and go home. By the time I get there, a few patches wet with Eliminator will usually be all it takes to finish the job and start coming out clean. Don't put too much on the last patch, and you can just leave it that way for months. No oil. The corrosion inhibitors work just fine.