I've been very pleased with BreakFree on my guns and knives. I use it to clean gun bores for "light" cleanings -- it will get powder residue but not copper fouling (and probably not lead either).
Some people will say WD40 is not a good choice -- it is really a solvent and does not leave a long-lasting moisture barrier. Many people use it on thier firearms, though.
Will, I've switched to RB-17 for copper fouling. It's a gel, sticks to brush and bore well, and has a pine scent despite being ammonia based. Good stuff. (When I lived in an apartment and cleaned guns on the kitchen floor, my wife got *real tired* of the stench of Sweet's 7.62!)
When I really crud up a blade, I usually use 0000 steel wool with the BreakFree. I trimmed my shrubs with a khukuri (works quite well, don't know what the neighbors think)and it really crudded up (think of the blades on your lawn mower) and I had to take scotchbrite to it.