Hydrochloric acid as toilet bowl cleaner?

I have those tough brown stains at the bottom of the toilet bowl. I read a glowing report on some cleaner stuff. The MSDS claims its only active ingredient is hydrochloric acid. What are the issues related to that?
I assume that the bowl can tolerate the acid. Is that a safe assumption?
How about all the other parts of the system? The seal hardware? The cast iron pipe? I can flush the system, but not necessarily get all of the acid out of all the crevices.
I'm not the least bit interested in trading a stain for a leaking toilet.
Experiences with cleaning the deposits safely?
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On Tue 27 Feb 2018 12:19:01p, mike told us...

We use ZEP Acidic Toilet Bowl Cleaner that contains hydrochloric acid. I'm not sure what the strength is, however, we have used it for 7 years with no ill effects and it removes every possible stain we've encounter inluding the brown ring which gradually appears.
It's a commercial product and does require caution in using it.
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On 2/27/2018 4:28 PM, Wayne Boatwright wrote:

I think its about 15% or half the strength of muriatic acid used to etch concrete. Fairly safe to use. Don't get in eyes, on skin or clothing.
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On Tuesday, February 27, 2018 at 2:19:43 PM UTC-5, mike wrote:

I've used hydrochloric acid without any problems. I have ABS pipe, but I'd use it with cast iron. First, you get most of the water out of the bowl by pouring a bucket of water in. Then carefully pour the acid and work it around to the spots with a toilet brush. I left in on for about 15 minutes, then flushed. Have a bucket of water to place the brush in to dilute the acid.
No acid is going into the pipes until it's flushed and then it's being diluted with all the water. Flush a couple times. If you have those real hard mineral stains, that's the fastest, cheapest, easiest way I've found to deal with it.
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