The method of renaming weapons has changed since the original upload of this guide, so it is possible that it may change again.
I've updated the steps below and they are accurate as of version 0.41.20.

Locate your game install directory. To make this easy, right click in steam, and browse local.

once in your game installation folder, go to this directory:
ZERO Sievert\ZS_vanilla\gamedata

If you only want to edit weapon names:
Open weapon.json

IF you also want to change the attachment/modification names to match the weapon names, you also need to open w_mod.json as well.

There will be lots of what we call "blocks" of code in here.
Each block is the definition of each weapon.

At the top, for example, is a block labeled "ak_101".
If you then look under the "ak_101" code block, there is a definition for "name".

Simply change all of the "name" definitions if you wish to name the guns to their real life counterparts. For example, changing the line under the "ak_101" block that reads:
"name" : "EC 101",
To
"name" : "AK-101",

Do the same with weapon mods if you choose to change those. I will also link a pastebin of each of my currently modded files at the bottom of this guide.

Here I will list all of the weapon names in the order they appear in weapon.json.

I will NOT upload my modified files anywhere because:
A) any game update adding/removing/changing in any way any of the files that I've modified will likely overwrite the changes anyways
B) cause issues if a new update releases and the code ive changed the names for becomes outdated/b]

I know it sucks, but this is likely something you are going to have to manually change after every update

Weapon names in order of appearance in weapon.json as of 04/18/2024:
"name" : "AK-101",
"name" : "AK-74",
"name" : "AK-74U",
"name" : "AKM",
"name" : "Stechkin APS",
"name" : "AS-VAL",
"name" : "ShAK-12",
"name" : "AVT-40", <--- the AVT-40 is the fully automatic version of the SVT-40
"name" : "DVL-10",
"name" : "FAMAS",
"name" : "FN Five-seveN",
"name" : "G-36",
"name" : "Glock-17",
"name" : "OTs-14-1A (Groza-1)",
"name" : "OTs-14-4 (Groza-4)",
"name" : "M1A",
"name" : "M4A1",
"name" : "PM (Makarov)",
"name" : "MK-47 MUTANT",
"name" : "Mosin Nagant",
"name" : "MP-153 12ga",
"name" : "MP5",
"name" : "MP-133 12ga",
"name" : "P90",
"name" : "PP-19 BIZON",
"name" : "PP-19 VITYAZ",
"name" : "PP-91 KEDR",
"name" : "PPsH-41",
"name" : "Striker-12",
"name" : "Remington Model 700",
"name" : "M24 SWS", <--- or Remington Model 700 PCR???
"name" : "RPK-16",
"name" : "Santa AK-74",
"name" : "Sawed off double shotgun", <--- rename as you like
"name" : "SCAR-H",
"name" : "SCAR-L",
"name" : "Sa vz. 61 Skorpion",
"name" : "SKS",
"name" : "SPAS-12",
"name" : "SV-98",
"name" : "SVD",
"name" : "SVT-40",
"name" : "Tapco SKS",
"name" : "TOZ-34",
"name" : "TT-30 Tokarev",
"name" : "UMP45",
"name" : "KRISS Vector .45acp",
"name" : "KRISS Vector 9x19mm",
"name" : "VSS Vintorez",

Use at your own risk. If you copy and paste this after an update that edits any of these files it can potentially cause issues.

weapon.json
Real Weapon Names[pastebin.com]

w_mod.json
Real Modification Names[pastebin.com]
Real Modification Names[pastebin.com] - fixed some missed EC74 to AK-74

grenade.json
Real Grenade Names[pastebin.com]