This is just my own $0.02 and there's bound to be differring opinions...to each they're own, go with what makes sense and works for you.
PS. This question has been asked and answered at least 3 times in the past month or so...a search would turn up the results.
There's a couple of things that need lubrication in a GBB.
1. Bearing surfaces and contact parts that move
2. Seals
1. Bearing surfaces and contact parts that move
- rails, pivots, disconnects, sears, springs, plungers...all need to have a bit of lubrication so that they move/travel/reset nicely.
- guys have used MSO2 (molybendum-di-sulphide) grease, silicone grease, gear grease (usually contains graphite or teflon in a grease suspension), dry graphite (messy), white lithium grease, superlube (aka viperlube), silicone oil (various weights)
For bearing & moving contact surfaces I'd think that you'd want something "light" that will provide lubricity and "stick" to the surfaces you apply it to. In a GBB, grease won't really get flung around...but you'd want to avoid clumps/build up. In general, you'd want to avoid substances that will trap dust/dirt (and really fine sand)...which will turn it into a fine grinding paste.
Alot of bearing & moving contact GBB parts are metal. But not very good metal. They're made from either monkey metal (aka white metal, pot metal), aluminum or steel (and most times pretty low grade steel). Sometimes these parts are "chromed" to put a harder/smoother surface on them. Regardless, they need lubrication. Not a lot, just enough to do the job and no more.
2. Seals
There are a number of seals in a GBB system, typically:
- magazine bottom seal
- magazine top seal
- magazine fill valve seal
- magazine main valve (aka knocker valve)
- blow back unit piston head seal with nozzle
- nozzle tip with hopup rubber
- hopup rubber with inner barrel
- float valve with interior of nozzle
All of those seals need to seal repeatedly and consistently for your GBB to work. Most (I think the only common exception is the float valve) have an o-ring/rubber seal.
So...any lubricant that will destroy rubber (i.e. petroleum based) isn't going to work. Many of these seals are not easily accessible...so lubricant needs to penetrate and "seep" into these areas. Similar to grease trapping dirt...you really don't want a lubricant that will "attract" dust/dirt that will wear at the seal. Drop your GBB mag on the ground...pick it up and use it in your GBB and you've just blow any dust/dirt that was on it right through the whole system (not the end of the world...everyone's done it and nobody keeps their stuff in hermetically sealed NASA food ziplocks
).
So...what to use....?
- lightweight (1wt to <15wt) 100% silicone oil...that's a good easy one that can be mixed with propane. Used this way, the oil will penetrate throughout the mag and get blown up through the rest of the GBB. With every shot, escaping "oily" gas will typically deposit oil over the entire firing assembly and usually it'll get to the rails and other parts as well after a bit. It "evaporates" after a while...so that's good in that it's not picking up dust endlessly.
- lightweight (non-petroleum based) grease on pivot/springs/bearing surfaces...a little goes a long way.
Maintenance:
- keep your mags with a bit of "oily" gas in them...don't keep them full, anywhere from Full-5 shots to just a shot or two left (don't know how to measure that) is fine. If you shoot a lot (i.e. every day or several times a week) you probably won't have any issues with storing them empty.
- learn how to fully disassemble your pistol (not just field strip). It may seem daunting because there's a billion little spring and screws in them...but after a season you'll be amazed at the crud build up in them.
- field strip clean your pistol after it get's a good workout....that might be after a single game for you....or after a month of casual plinking in the basement. It is NOT like a real piston where it's filthy after each use.
- Store it safely. No BBs in the mag, pistol locked up in a locked case and stored out of sight. Keep a pair of shooting glasses (they're dirt cheap and easy to find) in your case if possible...then you'll never forget to put them on when you're shooting.
Again, just my $0.02...use your common sense. No matter how bad you screw it up, someone's already done worse.
Best of luck,
Tys