For an overview of 10mm pistol models, see 10mm pistol.
“Small, dependable, reasonably powerful and widely available, the 10mm Pistol has been a staple of Wasteland combat since the bombs first fell.”— Fallout 4 loading screens
The 10mm pistol is one of the first weapons found inside Vault 111 (after the security baton), located in the overseer's office. The pre-War pistol does reasonable damage.[1] It also allows for a fair amount of modifications that further emphasizes its versatility. However, despite being provided with a substantial amount of ammunition in Vault 111, ammunition in the early portions of the game afterward is rare.
Vault 111, in the overseer's office. One will be on the desk and another will be on a shelf next to the case containing the Cryolator.
Sanctuary Hills, in the shower in the second house on the righthand side when approaching from Vault 111. Further 10mm pistols will usually be found in Sanctuary as random leveled loot.
Monsignor Plaza, in a closed curio in the upstairs gun shop.
Hub 360, in the DIA cache that may be accessed from a side alley fire escape and collapsed building debris.
Can be bought from most weapon vendors and usually from general traders.
Notes
Despite the long barrel modification being considered the "standard" for the weapon, the majority of 10mm pistols spawned in the world use the short barrel, similar to the .44 pistol and the Deliverer.
The two 10mm pistols found in Vault 111 both share a rare quality, in that whenever they are picked up, they will automatically be equipped, replacing the currently equipped weapon. This occurs even if the weapons are modded and renamed.
Bugs
PCPlaystation 4 When the standard magazine mod is detached from a weapon, that mod cannot be re-attached to any 10mm pistol (including the one it came from). In order to remove a different magazine type off a 10mm pistol, either a new standard magazine must be crafted, or a different magazine type must be swapped on to the pistol in order to obtain the desired magazine mod. [verified]
Gallery
Modifications: long light barrel, standard grip, standard magazine, reflex sight
Modifications: long light barrel, comfort grip, large magazine, suppressor
Modifications: long ported barrel, comfort grip, standard magazine, reflex sight, compensator
Modifications: long barrel, sharpshooter's grip, standard magazine, standard sights
Modifications: long ported barrel, sharpshooter's grip, standard magazine, recon scope, suppressor
↑The Art of Fallout 4 p. 236: "The base 10mm, for instance, is a different design from the version in Fallout 3. But with the proper mods, you can transform it into something very similar."