I've just done some of the maths for my character, and his main gun is absolutely ridiculous and I love it. 
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Assuming each bullet weighs 1kg, not including powder and casing (although their not very much, maybe 100 grams each), the bullets would have to travel at over 90x the speed of sound (over 19 miles a second) to have the same impact as described.This could cross the length of Manhattan is about 0.7 seconds. 6 of these in a clip, plus probably 35kg for the gun, means that Raiden has to carry over 41kg, not including spare ammo, other weapons and other equipment.
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