We added a new aspect to all items called 'hurt time' which is a variable that controls when the player can next get hurt.

All guns are 0.5 hurt time- let me break it down for you
So your Souizen does 8 damage which = 0.5 (hurt time) * 7 (7 hits is 54 hp, enough to kill this person) takes 3.5 seconds to kill this guy.
0.5 * 7 = 3.5 (simple right)

Now you also reloaded in this video clip, which made you wait 0.25 seconds (the freeze rate of the Souizen)

Now damage is based on the other persons lag, so for example if you're not lagging, but the other guy is (depending if they're on WiFi or 3G, same applies to you). If you see the bullet hit on YOUR screen, doesn't mean that the other player see's it hits them on their screen at that exact time.
This is the downside to clientside hit detection, but it's the best way.

I hope this makes sense