Equipping weapons in Red Dead Redemption 2 isn’t quite as easy as it seems because you are carrying weapons on you, but you’ll also be carrying weapons on your horse. You character will always have your sidearms available. These pistols can always be accessed via the game’s weapon wheel.
To access these weapons, press the LB/L1 button and then select whether you want your left or right sidearm, or you can choose to dual wield. In this weapon wheel when without your horse you will also be able to select throwable items like the lasso, throwing knives, dynamite, and fire bottles. You can also access melee weapons like your knife or others that you find like the Viking Hatchet.
To access Rifles you’ll need to take them from your horse to keep them on your person. Simply go to your horse and hold the LB/L1 button and select which weapons you would like to take off of your horse. You can take two rifles and carry them on your own. Any other weapons you have will remain on your horse.
When you are riding your horse you can access all of the weapons that you have on you and in the horse’s inventory. The weapons in each slot can be toggled by pressing the LT/L2 or RT/R2 buttons to select which weapon you want.
The important thing to know here is that you have not lost your rifles if they aren’t in your inventory, they are likely in the horse’s inventory instead. If the horse is close by just head over to it to you can grab your weapons. If it’s not close by you’ll have to make do with what you have on you.