Ha ha!! Nice story majid! 
In US, calibers are said using two digit or three digit numbers which show percentage of an inch. Here are some examples of how they are pronounced in English:
.22 ===> twenty two
.270 ==> two-seventy
.300 ==> three handered
.30-06 ===> thirty-ought-six
.404 ====> four oh four
In Europe, they useally use metric values for calibes, so they have calibers like these: 6.5x55, 7x64, 7.62x51, 9.3x74 etc. The first number shows the bullet diameter in mm. The second one is the length of the پوکه in mm.
The gun in this video is Caliber .404. In US, this caliber is known as .404 Jeffrey. In England, it's called "404 Rimless Nintro Express"!! and in the rest of Europe it's called "10.75x73". It is three times more powerful than a Kalashinkov and about 1.5 times more powerful than my 7mm magum:  
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