1918 Mexican Peso Identification Question

Hi,  could someone help me with this coin please?

17.33 grams

1918 Un Peso - Mexico

It looks copper or brass with silver plating that has started to wear off.  

Is that possible, does the weight make sense? 

I thought it was some type of corrosion or rust, but on close inspection it really looks like brown beneath the silver is showing through at wear points, rim, edge, etc.  I can measure the diameter.  I believe silver weight should be 18.13 grams and not sure if this is indeed copper, the weight would be only a gram off from the silver.  

I'm questioning if it is real or not.  There is text along the rim which also clearly looks brown copper or brass. Thanks

N#22317

the most likely one, I’m not sure though the images are not that clear

On this one, I think it is a copper pattern and was plated in silver. Because it looks like copper where the silver wore down.

Another theme here. Where are you aquiring these from?

https://en.numista.com/forum/topic177037.html

For this one, I posted this thread over a year ago but never really got an answer on it.  

I thought it was silver but clearly looks to be copper with the loupe.  It's not fake.  
So I'm assuming it is a pattern of some sort.  

Acquired decades ago and started to go through some of it now.  

That's all I have for now.  

Or perhaps you have the 1918 version of this one but copper given the weight you provided.

N#539553

Could be but the picture on your link looks fake and blurry. Thanks.