At least it seemed odd to me.

There was a dealer, had a bunch of Oly AR's on a table brand new.  Next to one was a 20rd mag that he said came with the rifle from Olimpic Arms.

This mag looked like the top part of a 20rd and the bottom half of something else 10rd???  It was clearly two mags put together.  Had the cut line and 3 rivits?? you could clearly see.  The floorplate said Armalite.

|------------|
|            |
|  Top part  |
|   of mag   |
|            |
|            |
|   *     *  |
|------------|
|         *  |
|            |
|------------|

My picture sucks but this is where you could see the cut lines and rivits.  Weird...anybody else ever seen anything like this?

Well this board does'nt show spaces evidently.  Here is a crude scetch and there may have been 4 rivits.
[img]albums.photopoint.com/j/View?u=1161949&a=8545098&p=45415250[/img]

The "Frankenmags" that came with the Bushmasters look like that.

Why cut a 20rd mag and stick a different bottom half on it?

Since they can no longer sell NEW Hi-cap mags they take new 20 rounders and modify so they are only 10 rounders. I have heard that Bushmaster is now making 10 round mags that aren't a butcher job.