I have a Thermold Mag that does not have the cutout (notch) for the magazine catch. I tried to seat it and nothing would feed, pulled it our and no notch. This was a new mag that was purchased years ago, I just finished going through the other 17 that I bought in that order and they all have the notch. The ones that are fine are marked Ar-15/M16. This mag has 1H on one side and just an H on the other. Any idea about what is happening here?

Could it be an AR180 magazine?  Pictures please of the rear spine.

Compare it to the ones they make for a mini 14

I added pictures of the spine. I would agree it does appear that it must be for a mini-14. It was from a box of Mags that a friend had ordered and couldn't sell on Craigslist and so he sold them to me for a killer price. Whoever he bought them from must ahve had this mixed in, or didn't know the difference and it was boxed up in the order. Thank goodness only one of them isn't for an Ar15.

Thanks again for the help, it is nice to know what it is!