To set up, we will need AutoHotkey, a popular scripting language for easy keyboard shortcuts and macros.

You can download AHK from their website here[www.autohotkey.com]. Once you do that, install using 'Express Installation' and close.

Then go to your desktop and right click -> New -> Autohotkey


Then, right click on the new file and click on 'Edit Script'


You should now have a file open in Notepad, if not, open it with Notepad. There will be some text already written in the file, ignore that and paste the following code below it.


Now save it.

What each line does:
o:: // Bind the 'O' key on your keyboard to start the script
p::exitapp //Bind the 'P' key on your keyboard to stop the script and exit AHK to regain Mouse and Keyboard control.
Send {x down} //Press the X key down
Send {x up} //Lift the X key up
Send {z down} //Press the Z key down
Send {z up} //Lift the Z key up
Sleep, 10 //Wait for 1/100th of a second
Click, down //Click the LMB down
Click, up //Lift the LMB

In Garry's Mod, open any single player map, open the developer console and type the following:

This will make it so whenever the X key on your keyboard is pressed, it will spawn the prop "metal_panel01a"

Go to the menu and equip the Remover.

Now alt-tab to your desktop and right click the AHK file and click Run Script.

VERY IMPORTANT
If you press the letter O on your keyboard from this point onwards, the script STARTS.
The only way to stop it is to press P
otherwise you will have to restart your computer since you will not be able to do anything.

Now, open Gmod look at a wall or a vertical flat surface and press 'O'. You should start spawning and removing the prop.

The script is not perfect and the game starts to lag in about 5-6 seconds . As soon as the game starts lagging, press 'P' and give the game a second to stop lagging. Now you can clear props using the menu and remove all the props using the Remover.
And then alt-tab out again, press Run Script, hop back in, and press 'O' again.

Thanks for Wildfire in the comments for making a better script
The script shouldn't cause the game to lag anymore as it presses 'Z' which undoes placing the prop.
So you should be able to keep the script running until you get the achievement.
I've tested the script on my end but if it doesn't work comment down below and I'll try to help you to the best of my abilites.

I found this method to be faster and more importantly doesn't strain my hands and fingers, and doesn't destroy my mouse.

If you have a better script for this, send it my way and I'll add it to this guide :D

Thank you for referring to this guide :D
If you feel there is an easier way to complete an achievement, or you feel the information provided isn't accurate please comment below and let me know;
and if you enjoyed the guide or found it helpful, please give a thumbs up!

Happy Achievement Hunting!