For what it's worth, I've just ended my test. With all of the comments on the forum about WD-40 gumming things up or solidifying into something that blasting powder can't dislodge and how WD-40 will totally screw up any gun that it is sprayed on, I did a test. It might not be the best test and it didn't involve anything that was rusty but it should have shown that after all thinning solvents have evaporated it becomes some sort of a solid that could do those things. The test involved taking the metal lid off of one of my old tins of CCI percussion caps and spraying the WD-40 into it to a depth of a little less than 1/16" deep. To give it something to bond in place I degreased a steel washer and tossed it in. I set this out on my BBQ in the hot Arizona sun figuring that not only should the heat evaporate all of the solvents but sunlight being what it is, anything that might solidify because of ultra-violet radiation would become semi-solid. (Tru-Oil drys and hardens in less than an hour in the Arizona sunlight.) After 5 days of sitting out there in temperatures that reached 114°F in the shade yesterday I will say the amount of fluid was greatly decreased. Now there is only enough to dampen the bottom of the lid with a small fillet around the corner where the flat area meets the sides. So what is this stuff that is left? If I were to give my best description I would have to say, oil. Very close to 30w oil. The washer is still wet from the oil and it easily moves around if I touch it. Based on this I will say that in my opinion, WD-40 leaves a medium weight oil behind after it has "dried out". A lot of things like tumbler locks use springs under the tumblers that are so light that 30 weight oil will tend to "gum them up", but for anything on a muzzleloading gun I don't think using it will cause any problems whatsoever. And now, let the debate begin. PS: I will keep the lid and washer inside for another week or so to see what happens in a nice, cool, refrigerated house and let you all know what happens.