I ran out of ammo at the end with Wesker, so I treated Wesker to about 30 slashes of my knife. It was funny because he would just keep picking me up, I would defend myself, then slash him some more. Over and over... 

I ran out of ammo. So, when I died, I craftily upgraded the cheapest part of all my weapons to get full clips all around. And I beat him with penultimate bullet of my rifle.

I can't believe they didn't put at least one or two crates. :(

Loved the game though. The Wesker fight was brilliant, I loved the way it made you think you'd beaten the game about 4 times, before throwing in another section.

I killed him with the knife in my first play through  in second one however , I had enough ammo for the whole fight . I am currently on my third play through with infinite ammo for L.HAWK magnum so ammo is no longer my concern .

nope, but I did try it because me and my friend did run out of ammo in our first couple attempts. We both just ran up and knifed him but got pwned quickly so I just thought it wasn't possible to knife his ass to death.

I ran out of ammo, and then I found out that you could restrain him. So, I grabbed him and then my bro did a QTE and stabbed him to death.

Is it possible to knock him into the lava? One of the parts of the area almost leads straight down into it (not a drop off, it almost sinks into it), and you can knock him back by shooting him in his weak spot. I was thinking you had to go all Terminator 2 on him.

You can restrain him?

I made sure I had at least 25 shotgun shots so that wasn't  problem for me. I'm on my second playthrough now so maybe I'll try something different.

Yep. I had to knife him to death.

"You can restrain him?"

I find that battle to be easier with the knife.  Reminds me of Krauser from RE4.

The only reason I died at all in that last stupid battle was because I didn't go to the right area to trigger the  cutscenes.  Like I would not go to the "high ground" and would instead first go the epic boulder so I was trapped.  I did the whole restraining him the first time.  I didn't know that a lot of people missed that.  I had more ammo troubles in the beginning of the game because I foolishly did not use the handgun and mained the mg's.  By the end I had a lot of ammo after i started using the rifles and shotgun.

i am playing it right now and i have a feeling i am going to have to knife his ass to death...or use the stun rod.....

The dude can take multiple handcannon rounds that do about 5000 damage whilst the knife does 50. Im guessing the knife must be really effective against him if you have managed to kill him like that.

I only had a limited amount of ammo, It took me a couple of tries to get my accuracy good enough to take him down with the limited ammo I had.

Nope, I didn't even come close to runnng out of ammo.

I never used the knife against him, I thought the only way to kill him was to restrain him, I was very low on ammo though. I had about 15 shots left in my Shotgun though.

I killed him with the knife the first time because I thought he was the certain enemy you had to kill with the knife to get the achievement. I was pretty devastated when I found out I could have got those points much earlier with the lickers.

I killed him with a volcano

I had no ammo problem. My issue was trying to figure out when it was okay to jump across the gap (i was playing as Sheva with a friend playing chris). We determined that you can't pull yourself up until wesker has jumped up on Shevas ledge, and after Chris shoots him a certain amount. In figuring this out, the two of us died at least 20 times.

I beat him with a (Spoiler).

I beat him with bullets and thought that he was too easy. I did like the game though

I kept using all my ammo, until I realized that realistically, you can probably only use ten bullets and beat him.

It isn't necessary to kill Wesker with a knife to obtain the achievement. It can be done by stabbing lickers.

Me and my buddy killed Wesker in the area with all the rocket launchers. He pulled out a rocket launcher and shot him and he grabbed the rocket, and I ran out and knifed the rocket! I think that counts..

I was close to having to resort to the knife.  Ammo got VERY low at the end.  I ended up having a few pistol rounds and my friend had no ammo whatsoever so he was running around like a pussy while I managed to kill him with one of my last shots.  I was surprised they didn't throw some ammo out there at some point.

I haven't played that far into RE5...because what I have played sucked...but I'm curious about your title.  Is mentioning Wesker REALLY a spoiler?  I mean, doesn't the whole world know that Wesker is the bad guy?  I figured that you know who with the hood would be the real spoiler on this...