[kingjoey]

Looks like someone welded a 20rd mag body on the bottom of a chopped mag. Find the guy out there selling a bunch of mag springs and followers and you'll have your culprit

 

[Landpimp]

my guess is Max Capacity is the maker, they are the only ones(I can think of) that make a mag that looks like that besides HK(UK, with tit)

the welds do look kinda rough though

 

[edman99]

I agree. They look like Max Capacity. Their products work pretty well.

 

[osprey2one]

A pic of the back. I've not seen one like this before

 

[BIGDUKE60]

if they have BLUE finish they could be max.
any probes with them. just swap out the follower with a Hk follower.
(or tweek the max one)