Help with new ammo types

So I have been at adding new ammo for a mod for a while now to no success, does anyone have any ideas of any good guides to follow or a mod I can look at? I’ve looked at the code and replicated from there but it doesn’t work. It just spits out this error message.
[const T& string_id::obj() const [with T = ammunition_type]] Tried to get invalid ammunition: 939
Again if anyone knows how or of any resources that can help please share away!

I mean, it would help if you showed us the code you are using.

Well, there’s the guide for first time contributors which discusses adding new guns in the section on new items.

Ya sorry forgot to post the code… here it is
“id”: “9x39_SP5”,
“type”: “AMMO”,
“name”: “9x39mm SP-5”,
“description”: “A Soviet designed shell using the 7.62 case with a sligtly longer neck. Developed by Nikolai Zabelin it is a conventional lead core FMJ bullet, developed for accuracy.”,
“weight”: “17 g”,
“volume”: “150 ml”,
“price”: 20000,
“material”: [ “brass”, “powder” ],
“symbol”: “+”,
“color”: “white”,
“count”: 30,
“stack_size”: 10,
“ammo_type”: “939”,
“casing”: “762_casing”,
“range”: 14,
“damage”: 31,
“pierce”: 5,
“dispersion”: 50,
“recoil”: 750
“id”: “9x39_SP6”,
“copy-from”: “9x39_SP5”,
“type”: “AMMO”,
“name”: “9x39 SP-6”,
“description”: “A soviet desogned shell using the 7.62 case with a slightly longer neck. It was Developed by Yuri Frolov it has a hardened metal armor-piercing core. It can penetrate 2 mm (0.079 in) of steel at 500 meters.”,
“price”: 20000,
“relative”: { “damage”: 40, “pierce”: 8 }

Where’s your definition for the “939” ammo_type? It’s not defined in the game or any of the mods from the CleverRaven repo.

Ah that would be problem, I thought I had to make it like that. There’s no mod for it out there