Kingdom Come: Deliverance II

In order to unlock the ‘Original Gunslinger’ achievement, you first need to go on a bit of a shopping spree. Firstly, you need to get yourself a Noble’s Belt, which is sold by Kuttenberg tailors for around 180 Groschen - this allows you to equip 4 weapons at a time (using the quick select menu).

Secondly, you need to visit Master Prokop Eldris, who is Kuttenberg’s gunmaker, who can be found south of The Hole in the Wall Tavern in the southeast corner of Kuttenberg - outside the main walls of the city, in an area called the Hoprink district (there’s a fast travel not too far away, to the east).

Now, before you buy 4 guns, make a save by exiting the game - otherwise you’re just throwing gold away, because there is no reason to have more than 1 gun, except for this achievement.

Then, load back in, buy 4 guns (3 if you already have one) and head outside - it doesn’t matter which 4 guns, they all count. Finally, equip all 4 rifles on your belt, and then systematically load all 4 of them, one at a time. Once you’ve loaded the 4th one, the ‘Original Gunslinger’ achievement will unlock.