Red border weapons in Destiny 2 are better known as Deepsight Resonance weapons. Certain crafting materials can be extracted from these weapons, and performing multiple Deepsight extractions on a particular weapon will unlock that weapon's pattern for crafting. Here's how you can farm red border weapons in Destiny 2.
How to farm Deepsight Resonance weapons in Destiny 2?
Sadly, there isn't any specific way to farm these Deepsight Resonance weapons. The drop rates for such weapons are strictly RNG driven, so you will have to be lucky in order to get your hands on one of them. However, any activity that drops legendary weapons, has a chance of dropping Deepsight Resonance weapons as well.
So, all you need to do is start farming activities like The Wellspring and complete all the playlist activities like Strikes, Crucible, and Gambit. If you're lucky enough, they'll keep dropping Deepsight Resonance weapons from the loot pool.
Alternatively, you can also explore the Throne World and complete Public Events, loot Lost Sectors, and Region Chests. These sources also drop Deepsight Resonance weapons, but the drop rate is slightly low, based on what we've noticed. Finally, while exploring the Throne World, you will come across several yellow-bar enemies. If you're strong enough, you will be able to melt these enemies in no time. And on rare occasions, you can also get these Deepsight Resonance weapons from the chests these yellow-bar enemies drop.
Now that you know how to farm for these weapons, check out How does weapon crafting work in Destiny 2: The Witch Queen, explained and more on Pro Game Guides.