no... no no no
20mm AA?? thats ok BUT......... try 25mm to 50mm(thats some heavy shit)
ok now my first look i was gunna say some where near 22 but then i had a closer look...(also size comparson) and you didnt realy give us a look at the Bottom... or the perfect top.. but then i scrolled down.. and then a nice image of different Amunition and a better look... Yes 357 magg... Military uses 9mm and Assualt... Cant remember their size...
A revolver.. yeah Sure... have the right size, this can come out of a Semi auto Pistol or any thing realy.. Nothing is to big

..
AA Bullshit... Nope.. not even close... This could not take down a Aircraft.........
now 7.65.. lol NOOOO :P HAHA
i got a 7.62mm Rifle... trust me No where near it...
i got 7.62 Rounds for all u boys who say oh its 7.62 ammo..
Pics:
From Wiki
http://upload.wikimedia.org/wikipedia/commons/thumb/d/df/NATO_7.62x51.jpg/300px-NATO_7.62x51.jpgFrom my Ammo Case
http://img2.imageshack.us/my.php?image=weaponry.jpgHand Packed by urs truly
These are most of the time Mistaken for .308 NATO's