Fallout 4

In-game console command method:

Step 1. Open the in-game console
Step 2. Enter the following command: player.placeatme 00038C1E 1
Step 3. Exit the console and face the newly spawned Ammo Box
Step 4. Enter the console, select the Ammo Box and enter the command: lock
Step 5. Exit the console and lockpick the Ammo Box
Step 6. Open the console and enter the command: lock

Repeat steps 5 and 6 until you have acquired the achievement.

I found an easy location to farm lock picks was at Fiddler's Green Trailer Estates. Which is a fair way due south of Sanctuary and just slightly north-east of Fort Hagen. Both the terminal and the safe next to it are novice. There are only a few ghouls that require to be killed to access this area.

Here's a video from MAKA91 which outlines the location and solution.

As you open your map on pipboy you'll notice 'black & white' lines going horizontal & vertical along the edges.
Go 4 white lines from the left & down 5 white lines & you'll find 'Jalbert brothers disposal' clear out the enemies & within the warehouse you'll find a desk with a terminal on it & to the left a safe on the floor.

The safe has an expert lock, the terminal is set to advanced.

Pick the safe then hack the terminal, within the terminal you can relock the safe & then pick it again, repeat untill achievement pops.

There is also another location just southwest called 'arcjet systems' that has two more set ups like this, one has an expert terminal & an advanced safe & the other also has an expert terminal but I think it was a novice safe if I remember right. However above the safe is a cabinet with the password for the terminal so this may be the best option for people with a low Bobby pin count or a low lock pick skill.
However, to reach this one

Open the console command window with the ~ key (on US keyboards). Type in the following command:

modpcms “Locks Picked” 50

Achievement pops after a short delay. (10-15s for me)

An alternative for anyone wanting to explore another unused area and get this done.

If you don't have lockpick 4, why not give it to yourself by typing the following. So as not to mess things up, ONLY USE THE ONES YOU NEED! If you have locksmith 3, ONLY use locksmith 4's command. Only use each command once.

Use the ` key or regional equivalent to open the console.

Locksmith 1: player.addperk 000523ff
Locksmith 2: player.addperk 00052400
Locksmith 3: player.addperk 00052401
Locksmith 4: player.addperk 001d246a

If you happen to need a bobby pin:
player.additem 0000000A (with locksmith 4, it won't break)

The location we'll use: Terminals & holotapes, o my!
coc zUnusedSubwayTerminalShowcase

tgm (for God mode, or at least be aware there are enemies here)

Follow the linear path and defeat the enemies (Raiders and a turret as I recall.) You'll come to an end where there are doors on the left and right. Go right. Pick the safe instead of using the terminal to unlock it. Since you have locksmith 4, you won't break the bobby pin. Once you open the safe (and raid it if desired) use the terminal to relock it. Thankfully its the top options so you can get a good rhythm of mashing and returning to the safe. Repeat until you get your achievement.

You can also find some unused holotapes when exploring. They are in the same room as the safe we used. They are Turret_override.exe & RobCo defragmenter. One is in the safe and the other is on the table the terminal is on. Just noting because its why I went to this room. Also, the terminal supposedly opens the other door here. I never got it to work. I cheated with no clip to get through. Its a bit of a mess so save before trying. Toggle it again to return to reality. The command is: tcl

This solution assumes that you know how to use the in-game console (accessed with ~ or @ and some other keybinds depending on your region) and that you have progressed past the opening of the game out of the vault and into Sanctuary. You can check the keybinds from the main menu if you need to refresh your memory.

-If you want to get this without console commands, you are likely to unlock it by exploring and unlocking containers over time in your playthrough

1. Load a game / be in game (I think you have to progress through the opening section of the game to get some of the achievments)

2. Now you will spawn a container by copy+pasting in or typing: player.placeatme 00038C1E 1 (and then hit enter)

3. Now give yourself lockpicks by typing/copy+paste: player.additem 0000000a 2500 (and then hit enter)

4. Enter the following commands, ignore the text that appears about "rank 1"

player.addperk 000523ff
player.addperk 00052400
player.addperk 00052401
player.addperk 001d246a

5. Exit the console, look around you and you will see an ammo box

6. Open up the console again and click the ammo box & it will now say " (ff001894)] -or- ff000fff in white on your screen

7. Type in/copy+paste: lock and enter the command

8. Exit from the console again now approach the container, it should be locked, if not try again-- now press the prompted button (E on keyboard) to enter the Lockpicking interface

9. Follow the onscreen tutorial or reference this video/image if you don't understand how to do the lockpicking minigame. You basically need to open each lock, rotating the bobby pin and applying pressure with the screw driver, adjusting the angle of the bobby pin to reduce resistance until you find the right spot and the container opens

-Tutorial image:

-Tutorial video:
10. After you successfully lockpick and open the container, exit the Search interface, re-enter into the Console and enter the lock command again (making sure that (ff001894)] is still white on your screen, click the container again while in the console to make it so if necessary)

6. Lockpick the container again. Repeat this until the achievement pops, for me it was about 15 seconds after the last lock.

You can check your progress by going to the pip boy/main menu then navigating to DATA - STATS - CRIME.

just use console command

modpcms "Locks Picked" 50