Somewhere on this site is a good write up and a bunch of pictures.

Look in here https://1919a4.com/showthread.php?39718-WTK-MK-21-Mod-0-Machining&highlight=Mk21+Mod0


This isn't the thread I recall but might be a good start.

At least it will gain some attention for your topic.

 

Thank you !

 

Gabriel--
I can help you out on this project. I really tried to get down in the weeds on this one 6 or 7 years back. I even tracked down the head of the original design team, Mr Ronald Henry, who still alive at the time and had been retired since the 1970's and we spoke for several hours over the telephone about the development of the MK 21 Mod 0 7.62mm Browning MG modifications. As far I know there is only one gun that still exists in the hands of one of our members here. In my research I could not find one in any of the Ordnance Museums here and abroad.

--fjruple

 

MK21 Mod o

I had picked this scrap up at an MV swap meet a long time ago...
DanG