Those MKE mags need for that "LIP" that runs all the way around them to be removed since it contacts the lower mag well lips, which FIRMLY prevent it fitting into well!
I had to do that to all three of my MKE's so they would even fit the C-93. Then I inked the whole upper area on the mag that fits into the well, saw where it hit/contacted the gun most, and then SLOWLY started filing, then sanding, those same areas until it fit AND locked in place. These are INDIVIDUALLY fitted to my C-93 but work great. However each gun is different and 2 0f my 3 won't lock into a friends C-93 while the third is perfect in both guns.
Since they all work in mine now, I like them very much. I have three HK 30 rounders (new) from HPParts, and three HK 25 rounders (also new fro the Eighties and his HK 33) from a friend and they also fit first time/every time.
The 40 rounders I have (2 came with the C-93 and I bought 5 more from Keep On Shooting) are hit and miss as to staying in gun while firing.
The locking tab (and ALL other parts on this gun) look almost new/unused. Mine is a low serial number gun (under1000), and the number is on TOP of receiver rather than on the side of the mag well.
Gun DID have to visit GHILLIE before it would cycle properly, and to get the bolt gap to stop shrinking. No new barrel/trunnion has been installed yet and gap is steady around a loose .009".
Shoots great and groups as good, or better than most of my AR's.
(HOWDY BLITZKREIG !!!--HOPE YOU ARE ALL WELL!!