OK, I have been buying and saving M14 mags for several years, and finally got a poly M14 from a guy here on Arfcom.

The (Chinese)? mag that came with it seats fine.

The Midway "type 57 Taiwanese" mag (blued steel) that some on here have said are actually KKK's or other brands seats perfect. (I have five but only tried one).

The five parked ones that I got from 44mag don't seat very good at all.  I finally got them to seat by pounding the bottom of the mag pretty hard. ( They ALMOST seat, but stop just shy of catching until I smack them real good).

All mags were empty and the bolt was back.

Why are these CMI mags, which are supposed to be the best current manufacture, so dissicult to seat?

Midway USG "Type 57" magazines are not made by Triple K or ProMag.  I think I know who is making them but I can't confirm it.

Based on some measuring done by several of us M14 fans, a few Check-Mate Industries magazines are a hair wider at the top end (above the Y-Y line if you have the magazine drawings) than the drawing maximum dimension.  Those magazines won't fit in magazine wells with perfect (USGI drawing) width, e.g., LRB Arms and apparently, Chinese receivers.  

Quoted: Midway USG "Type 57" magazines are not made by Triple K or ProMag.  I think I know who is making them but I can't confirm it. Based on some measuring done by several of us M14 fans, a few Check-Mate Industries magazines are a hair wider at the top end (above the Y-Y line if you have the magazine drawings) than the drawing maximum dimension.  Those magazines won't fit in magazine wells with perfect (USGI drawing) width, e.g., LRB Arms and apparently, Chinese receivers.

That's good to know.  The Midway rep was sure they were as described, but could not absolutely confirm it.  He said his worked well.

I have your website bookmarked to check out further.

All the mags fit perfectly after one string of twenty rounds from each mag.  Except one Taiwanese one that was out-of-spec.