My only problem with the boiling (or really hot) water, is how quickly the barrel can/will flash rust. The first time I did it, it scared the bejeepers out of me, but I got it cleaned up. I’m a little “gun-shy” (no pun intended) now. How do you avoid the flash rusting?
I'm going to wager that you live where you get treated city water and that is what you heat up and then see flash rust when you clean.
I have city water and always have seen flash rust if I heated it at all. Anywhere from slightly warm to piping hot = flash rust. Room temp or cold, no flash rust. I find that tepid to cold water cleans just fine, but hot water is nice for how quickly it evaporates and dries in the barrel. I also like hot for dissolving animal fat based lubes I use.
Lots of other folks here have commented about cleaning and using hot water, some saying they always get flash rust and some saying they never do. The ones that I asked that did get flash rust were all using city water, and the ones that didn't get flash rust were on well water. I didn't ask a ton of folks, but enough to form a theory. Specifically, I think it is the chlorine that is added to city water that causes flash rust when it is heated.
Next time you shoot, try heating up some distilled water to use, rather than water from your tap. Bet you don't get any flash rust. I haven't had flash rust since I started using distilled water.