Ok, it really depends whether you're playing on co-op or single player.
Single player: A magnum probably works best, just aim for the head and KEEP MOVING. If you don't have magnum ammo just shoot him enough (from a bit farther pack) until he stumbles forward. Then, get close and use your shotgun.
co-op: Have one player get up close to distract him and have the other one snipe. Or, you can get him to follow one partner while the other continuously follows and shoots him.
Do you mean the one at the oilfield? Well I did it with a partner and took him down with the magnum. One goes down the zip line and the other sets up below where the chainsaw will appear then just take him out. I found a walkthrough vid but the person has unlimited launcher which you have to beat the game in under 5 hours to get but maybe this will give you an idea .Hope it helps.
well that depends what difficulty ur on, but the stadegy i use is pop of a few shots from the distance with the shotgun or if u can get some long distane from u and him u have the option of shooting him with sniper in the head a couple of times or try to distract him whil sheva shoots him down. This proccess will take a while and it wmight be a pain to do but, it works.
Basically you have to stun the chainsaw majini with a flash grenade & there the easiest weapons to defeat him is the rocket launcher grenade rounds magnums maybe the rifles can take him out easy but I will do a quick video about that question.
