I found the pieces from my intellidropper, and it looks like I had already scraped most of the powder off, and attempted to burn it at one point. As it turns out, burning it is not the way. There's a lot of pictures coming up with some text in between. Hopefully it's somewhat easy to follow.
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I found the hopper, and I had not attempted to clean that at all. It has been like this for at least two years. This was either CFE 223 or maybe Lil' Gun. Here's a picture of it in original condition, followed by an assortment of cleaning methods I tested on my lunch break today.
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First up, soap and water. This made the powder residue easy to remove, and didn't damage the plastic at all. It didn't remove much of the discoloration, but at least it was clean. 7/10
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I tried some 91% isopropyl alcohol on that same spot, which showed little improvement. Not worth the time, in my opinion. 3/10
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I tried acetone on a different spot. This turned the powder into a thick goo, and started to deform the plastic. -4/10
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CLR. Worked ok, didn't deform the plastic. Wasn't as easy to wipe powder off as just soap and water. 5/10
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Patch out & accelerator. Similar results to CLR. Kind of a waste, in my opinion. 5/10
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I had a few other solvents available, but not a lot of time left for lunch, so fire was the only option at that point. It lit slower than I expected, but once it lit, all of it went up fairly quick. It burned for a few seconds, then fizzled out, not changing much in appearance. 16/10, would certainly recommend.
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The top half of this picture is just burned, the bottom half is burned, then Patch out & accelerator.
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After all the exciting stuff was complete, I used hot soapy water and steel wool. This seemed to be the most efficient and effective way to clean the hopper. Again, it didn't take all of the discoloration out, but it removed any residue as far as I could tell. I'd feel comfortable using this hopper in the future, but might flip it over so the discolored portion isn't in contact with the powder most of the time. 9/10
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After this not so scientific test, I'd recommend disassembling everything, and cleaning it with soap and water first. If that doesn't remove enough of the residue, maybe try sanding it with a very fine grit sandpaper afterwards. I can try that later, if that would be any help.