This guide is for upgrading the sling. Get to Chapter 10. While it's loading, press and hold
until the chapter is loaded, then wait for a few seconds. Now, hold
, then highlight an already-crafted upgrade (if you don't have one yet for that row, highlight the locked one to the right. Then, while holding
like you normally would to craft ammunion, quickly select the one you want to craft, then keep holding
and
until the entire row is upgraded.
Here's a video showing it working:
I take no credit in the making of this video.
NOTE: When I did this on Xbox, I had made it to Chapter 14, then replayed Chapters 10-13 hoping to keep my upgrades. When I reached Chapter 15, my Chapter 10 upgrades were gone.
However, when I did it on PC, I used the glitch to complete the upgrades right when I got to Chapter 10 (through Chapter select obviously), and I was able to keep them for the rest of the game, allowing me to save my precious crafting materials for my weapons.
So try to go for these achievements before completing the chapter.