The muriatic acid is a diluted strength (to about 30%) of hydrochloric acid. Like most things, it will attack whatever is easiest, which is the rust followed by the soft metals, then the steel. So before it is even eating the brass strips, it has neutralized itself on the rust. I can only put a small amount on the surface due to the small space . I have elevated the trail to get the gun close to neutral elevation, have it tipped to one side slightly, and pour an ounce or two onto the front of the rail. I put a bit of plumbers putty at the back which helps retain a little of the acid to where it is needed the most. I was going to use RTV silicone, but the reactions of the two would not have been favorable. Seems like anytime you have the word "chloro" in the formula, it can be released thru heat or mixing of chemicals.
Phosphoric acid was the main ingredient in almost all of the rust eating products I tried, but if allowed to dry it converts the rust into a very hard material. Before going on holiday, I broke off small pieces of rust and sat them in small containers with samples of each product. When I came back, the piece of rust was still in each. Phosphoric acid is in Coca Cola, which is rumored to eat a penny or clean a toilet bowl. Doubtful as it is only at around a 1% solution.
I go out of my way to find the products that work. I still use solvent (mineral spirits) in my parts cleaning tank, and only buy the chlorinated brake cleaner. I take suitable precautions with each. I may well pay the price one day, but like the muriatic acid, I look for whatever works easiest. I find the words "environmentally friendly" do not always lend themselves to that requirement.
All that said, my days of sandblasting with a simple dust mask or respirator on are long gone. I now have an air supplied hood, which has the added benefit of keeping one cool on the warmer days.
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