These guys a brutal, the most effective way to kill them is with a shotgun, or a Thompson.
To kill them you want to use you grenades first if you have any, this is to weaken them.
Then you get your Thompson and keep you iron sights on him. But you really need to have the 50 round drum to do this cause it usualy takes 40-50 rounds to kill them.
If you have a shotgun and they are really close shoot them in cover, then charge shooting them to stun them until you get close enough to use the bayonet on your shotgun.