Lar-Those rounds are or are similiar to the 25mm x 116B mm. They are not the full bore 25mm x 137mm Bradley/Bushmaster round that is much bigger powder capacity and more common
in our military.Here is a link to a lot of different
shoulder fired military style big bore guns from different countries-Check out the recoiless 20 mm one.Full size 20mm.
http://world.guns.ru/sniper/sn61-e.htm .Ed

Oh, come on, those look about like my Howda rounds.