To say that any one weapon won world war 2 is a grandiose statement, and it shows that you don't have a very firm grasp on how the war was actually fought. It comes down to the people that used them, and more people used the Mosin Nagant than any other gun in any other theatre of war. I'm not saying that the Soviet Union won the war, that's not true, it was a combination of everyone. But the USSR had enough steam left over that they could have went to war with the US for the rest of Europe if they had wanted to. But they didn't want to do that until they had their own super bombs.

Of course we also have the Lee-Enfield, PPSh-41, StG-44 and all the merry weapons of WWII.

There we go! An international coalition of murder devices!

And of course the grenade

First thou pullest the Pin. Then thou must count to three. Three shall be the number of the counting and the number of the counting shall be three. Four shalt thou not count, neither shalt thou count two, excepting that thou then proceedeth to three. Five is right out. Once the number three, being the number of the counting, be reached, then lobbest thou the Hand Grenade in the direction of thine foe, who, being naughty in my sight, shall snuff it.

I always enjoy sniping with a Dragunov. Russians make prettier guns than Americans

Also, the Widow Anti-Materiel Rifle in ME2 and 3 is one of my all time favorites