How does weapon modding actually work?

[Jeff Kaos]

I understand how to add mods to my gear but what I can't seem to understand is how I have a sack full of weapon mods but when I try to add them to a weapon only one is available. The game does absolutely nothing to explain this. Why do I have 9 coils but only one is available when I mod a my bow?

EDIT
For clarity here's my current situation that's leaving me confused:

I just bought a Carja Sharpshot Bow that has 2 mod slots. I have several Flame Coils, several Shock Coils and a couple of Corruption Coils. When I try to mod the bow the only Coil I can select is one single green Fire Coil. I have absolutely no idea why that one coil can be added but not any of the other coils I have. The game doesn't really explain this and everything I look up online basically says the same thing: "There's a difference between Coils and Weaves and you're probably too stupid to know the difference".
That's not the case. I know the difference and it's pretty obvious. What isn't obvious, to me at least, is what limitations there are for adding specific mods to specific pieces of gear.

[DarkDevXx]

Coils are for weapons, Weaves are for outfits. You'll only be shown any coils available that will fit the weapon you're trying to mod. There are also Spear modifications which can only fit into the spear. These all look very similar in the Modifications satchel, but it's likely you have a bunch of Weaves and just 1 Coil for the weapon.

[Basan™]

You can't just fit any sort of Coil mod into all of your Horizon Zero Dawn (HZD) weapons[horizon.fandom.com]. And that link provides a better explanation than my mere example shown below.

As a mere example, the War Bows don't accept Tear (i.e., Broken Shield icon) and Damage (i.e., Arrow Point icon) Coil mods. And that's also because Tear doesn't have an impact upon such Bows' ammunitions (for ex., it always remains at 0 value no matter how other Elemental damage Coils may also add something into that dept).

[Jeff Kaos]

Originally posted by Darth Donuts:

Coils are for weapons, Weaves are for outfits. You'll only be shown any coils available that will fit the weapon you're trying to mod. There are also Spear modifications which can only fit into the spear. These all look very similar in the Modifications satchel, but it's likely you have a bunch of Weaves and just 1 Coil for the weapon.

I totally understand the difference between coils and weaves. And I have several of each. Here's the situation I have right now:
I just bought a Carja Sharpshot Bow that has 2 mod slots. I have several Flame Coils, several Shock Coils and a couple of Corruption Coils. When I try to mod the bow the only Coil I can select is one single green Fire Coil. I have absolutely no idea why that one coil can be added but not of the other coils I have.

[Death Approaches]

no it's not that you're too stupid, it's that you don't know - there's a difference between ignorance and stupidity. The former is curable, the latter, for life.

each weapon only does certain things, only shoots certain ammo.

I think your green one isn't fire, or maybe a combo coil exists in green, with tear or damage or handling on it too... fire arrows aren't fired from a sharpshot, that's not something it does, even if it's a combo coil, with fire and damage, it's not gaining the fire anyway, sharpshots are about damage and tear, do you have any coils for those, or handling? I'm guessing not, since none of them show up as installable. Do you have a hunter bow? Bet you can slot those others on that.

I put handling and damage on a blue sharpshot since I'm still at low level, and purple 3-slot gets all 3 damage-only coils; the extra second isn't going to matter as a slow sniping bow when I'm not detected... I lead with that, then switch to something that fires faster and has elemental effect if I didn't drop em.

It's working as intended though, it's not glitched, if that's what you're thinking.

[Bird_Dog]

Originally posted by Death Approaches:

I think your green one isn't fire, or maybe a combo coil exists in green, with tear or damage or handling on it too... fire arrows aren't fired from a sharpshot, that's not something it does, even if it's a combo coil, with fire and damage, it's not gaining the fire anyway, sharpshots are about damage and tear, do you have any coils for those, or handling? I'm guessing not, since none of them show up as installable. Do you have a hunter bow? Bet you can slot those others on that.

A fire coil will not show up as an option for moding a sharpshoot bow, that's right.
Even if there's a secondary effect that would benefit that bow, it won't show up. I just doublechecked.
The primary effect must be compatible.

@OP
Early in the game those coils can be quite rare (towards the end of the game, you'll be brushing your teeth with the stuff though...). be careful about putting them into weapons you will soon replace with a better one. Without the Tinkerer Perk you can't remove or replace modiffications. Once you reach Carja territroy you can buy Shadow Carja weapons (purple). Those will stay with you much longer.

[Jeff Kaos]

Originally posted by Death Approaches:

no it's not that you're too stupid, it's that you don't know - there's a difference between ignorance and stupidity. The former is curable, the latter, for life.

each weapon only does certain things, only shoots certain ammo.

I think your green one isn't fire, or maybe a combo coil exists in green, with tear or damage or handling on it too... fire arrows aren't fired from a sharpshot, that's not something it does, even if it's a combo coil, with fire and damage, it's not gaining the fire anyway, sharpshots are about damage and tear, do you have any coils for those, or handling? I'm guessing not, since none of them show up as installable. Do you have a hunter bow? Bet you can slot those others on that.

I put handling and damage on a blue sharpshot since I'm still at low level, and purple 3-slot gets all 3 damage-only coils; the extra second isn't going to matter as a slow sniping bow when I'm not detected... I lead with that, then switch to something that fires faster and has elemental effect if I didn't drop em.

It's working as intended though, it's not glitched, if that's what you're thinking.

Actually, I am kind of stupid. I have about 8 bows in my inventory since I have no idea right now what's worth keeping and I keep expanding my carrying capacity for everything whenever I can. Anyway, I was modding one bow when I thought it was a different one. So I was trying to mod a blue Carja Hunting Bow while I thought it was the blue Carja Sharpshot Bow I actually wanted to mod. I looked up the wiki page on weapons and the page on mods and now I think I have a decent grasp of how this system works. I just wish the game explained more than it does. I've had to go online to understand what a lot of the stuff on the map means.