Left 4 Dead

You have to begin at the very beginning of a campaign and go until its conclusion. This cannot be attempted if you start in the middle.

When starting, do not grab a gun. While you are traveling, do not grab a gun other than the second pistol and do not use a mounted Gatling gun. Molotovs, pipe bombs, and melees are ok and shouldn't disrupt the achievement. You won't have to worry about finding ammo as the pistols have unlimited ammo.

This is going to be substantially easier to accomplish on one of the easier difficulty settings. Finding a good group of friends will also make it easier.

Easy on low settings. Keep your pistol at the beggining, STAY AWAY FROM THE GUNS. Just make sure you pick up another pistol along the way. Use Pipebombs when you have them, and Molotav-ificate Tanks and Witches. Try to crouch behind the AI and shoot from there, as they get amazing shots all the time. The only part that may be troublesome is the finale.
No Mercy- Set out the gasoline tanks outside the ramp and hide under it. the AI should follow and its just wash rinse repeat.
Death Toll- Have the AI follow you to the glitched rock and just stand on it and the AI should knock out most of the Special Infected before they are a threat.
Dead Air- Sit on the hill with the AI. You get amazing shots here so its absolutly no problem.
Blood Harvest- Stay upstairs, close the doors. Put any explosives (gasoline or propane tanks) at the bottom of the stairs. Be sure only to shoot them when the Tanks come. Pretty easy with the three amazing AI.

Hope this helps! Leave any questions as comments or PM me!

Found a cheap way to do this while going for Unbreakable.

Split screen.. Crash Course... Easy

Soon as it starts up.. have the profile you want to get the achievement TAKE A BREAK.. letting the CPU take over.

Then with the other controller play through the game.. it seems that the CPU only uses pistols while they are controlling.

Fast forward to the end of Crash Course.. right before the end of the level as the truck is lowered I paused the game and switched it.. took control of my profile and let my other take a break.. Jumped into the truck and done.. popped.

This is a very easy achievement if you follow this guide you can also do safety first.

What you do is start a game up on single player on no mercy and if you don't fire you will be awarded with both achievements at the end of the game.

You still have your unlimited whack avaliable, so just whack zombies back and the AI team mates will take care of them, the only thing is watch out for tanks as if you whack them you do no damage get a molotov and throw it at the tank which will damage him and your team mates will fire at him also this will get you your towering inferno if you haven't already got it. watch out for boomers as well as if they get you will be surrounded by zombies and you will lose health.

Also if you feel like you will fire just don't pick up any guns and DO NOT use the gatling gun, molotovs and pipe bombs will not affect the achievement so if you have them use them regularly as they will help.

Hope This Guide Helps You.

Also If You Give Negative Feedback State Why In The Comments And I Will Try And Improve It.

Have four human players run through a well-known Easy campaign, all using pistols. You can pick up second pistols but don't even bother with a gun, and don't bother with throwables as it's not needed.

Once you run all the way through from start to finish, and complete the finale, it will award it to all of you.

Hope this helps.