Obviously you can't do this if you want to unlock this achievement.

One last important thing to note is that when you get to the guy on the machine gun, you'll be instructed to use flashbangs to blind him. There is more ammo for the 1911 at the section where the enemies light everything on fire and you have to climb the ladders, so at least if you can make it that far you can get more ammo there. There aren't many enemies in the tunnels, it's usually just one or two at a time, so just line up your shots well and you'll have plenty of ammo. So there is plenty of ammo as long as you aren't spraying bullets mindlessly. I personally unlocked this achievement on Veteran difficulty and still had 17 bullets left at the end of the mission, and I didn't get any additional ammo along the way. On higher difficulties, you'll need to manage your ammo. If you're playing on Recruit difficulty, this isn't an issue because whenever you die or reload a checkpoint you'll respawn with full ammo. The main challenge with this achievement is ensuring you don't run out of ammo. Using a melee on enemies is up for contention, but it's a safer bet to avoid that as well to ensure the achievement unlocks. Not only that, but there have been reports of the achievement not unlocking if you even pick up another gun. This means no guns AND no flashbangs, molotovs, etc. From here until the end of the mission, you must use no other weapons or gear except your 1911 pistol. After going down into the tunnels and a cinematic plays, you'll regain control and have one. Don't fret that you don't have a 1911 pistol. The first part of this mission takes place outside and in a couple buildings.

Call of duty m1911