It’s an automated MK79 - been around for a while ...
I believe that the 40mm grenades fired by the MK 19 are not interchangeable with the 40mm grenades fired by the M-79 or M-203.
The Russians always had a policy of naming ammunition by different millimeter numbers, even if they were in fact the same caliber. This was to avoid battlefield logistical mixups.
“I ordered the 40mm MK-19 rounds, NOT these #$%$^! 40mm M-203 rounds!! We can’t use these!”
In Russian nomenclature, one type would be called 41mm, even if it was 40mm, to avoid battlefield mis-shipments.
So I see. designed in the 60s