777 is water soluble so almost anything will work including plain H20. Water based products like Windex or Simple Green are more aggressive but don't let it soak for any length of time. There's no rust preventative agents in generic cleaners and they will rust the bore if left overnight. Don't ask me how I know this.
You also have remove all traces (thoroughly clean and dry) and apply rust preventative when your done cleaning.
I have a bottle of Cabela's black powder solvent that worked well cleaning 777 in the bore and with the breech plug. Water based ML solvents have a rust preventative so they won't induce rusting as quick as a generic water based cleaner.
IME, 777 residue is fairly inert and fouling won't cause rust in a short period of time (a few days or a week or so) as long as the bore stays dry. From my understanding (not lab tested by me) when moisture/water comes in contact with 777 fouling reside that's what makes it's corrosive.
Which bore cleaner is best? I dunno. There's probably as many good ones as there are ways to skin a cat.
With that said the way I scrub my 50 cal ML bore is to use a .45 cal bronze brush wrapped with a 2" X 2" cotton patch. This gives a far greater contact area and makes cleaning easy. This method works for centerfire rifles too.
This is also what I use to swab the bore between rounds with 777. One patch wet with water (moist not dripping wet) wrapped around the brush and one stroke down and back. Turn the patch over and one stroke down and back. Follow up with a dry patch once down and back. This provides a clean consistent but slightly fouled bore, eliminates the crude ring, and loading problems. I also believe it's the key to consistent accuracy when using 777.
There's one other issue that should be addressed if you're shooting sabots and that's plastic fouling. It probably takes many many shots to build up any appreciable residue but a scrub with a solvent that helps dissolve plastic once in awhile can't hurt. Birchwood Casey Bore Srcubber is a bore cleaner that claims to remove plastic wad residue. I like using it because it's not colored and it's easy to see when the patches come out clean.
Since I'm blathering and we're on the subject ...
I've switched to BH 209 and Dyna coated the bore on my TC Omega. I scrubbed it with JB compound and then metal polish to achieve a mirror finish before coating it. The last range session I shot seventeen rounds and each loaded as easy as the first without swabbing. When I got home I ran a couple of dry patches through the bore to knock the heavy stuff off and then let it soak for four hours with Wipe-Out. It took about eight patches to remove the goop/crud, get it sparkling clean, and back to mirror shiny.
Before the last range session I installed the breech plug using a very light coat of Super Lube synthetic grease on the plug, two wraps of teflon tape, and another light coat of grease. The breech plug broke loose with no more torque that I used to tighten it and it unscrewed as easy as went in. The flash channel was heavily fouled and needed a thorough cleaning with a drill bit.
Blah, blah, blah.
