There are a lot of guns in Borderlands 3 and you can easily find your inventory stuffed to the brim with them. Thankfully, Borderlands 3 allows players to not only upgrade their inventory space but the amount of ammo they can carry into battle. Tied to SDU’s sold by Marcus, these devices incrementally increase your carrying capacity, for a price. Unlocked once you leave Pandora on the Sanctuary spaceship, Marcus will begin to sell these once you put out some fires on his gun range.
After this is done, approach the large table of items underneath the Marcus Munitions sign. You’ll be able to interact with this table and select what you want to increase the carrying capacity of. Each item will only cost you $1,000 at first, but the price will dramatically increase with each subsequent purchase. Because of this, don’t expect to have everything fully upgraded until much later in Borderlands 3.
We suggest increasing your character’s inventory at least once so you can hold more items during your travels. The ammo is personal preference, but we recommend upgrading the Assault Rifle since this seems to be one of the most common weapon archetypes in the game. Remember, any time you feel like upping your reserves, just come back to Sanctuary and buy the needed SDU from Marcus.