basically the title says all: This marine demonstrates how to reload a M4 carabine in 2.61 seconds.
Marine reloads M4 in 2.6 seconds
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Revolver quick reload
This video shows a man shooting 6 shots from a revolver, reloading and shooting 6 shots again… in three seconds (2.99 seconds to be exact 
).
Fast reload of AK-47
This video explains a unusual but pretty effective way to quickly reload the AK-47 rifle. With some practice you can release the old magazine, attach a new one and reload within roughly 3 seconds:
The next video demonstrates the more or less “common” quick methods to reload the AK-47: