It so happens, I carry the gun, and it only gets 1 shot, even if I hit R, only gets 1 shot. But in my inventory 4 bullets were reloaded.
But if I replay, the weapon will appear fully reloaded. 1(+4) Like at the beginning of the video. https://youtu.be/RHCIDtZ86kc
Follow the marking on the video >

When I load and re-read, I get 1 (+4)
If I do not re-enter, I get 1 (0)
MY INVENTORY DISAPPEARS 4 shots
At 15, I load, go to 11, and down there is 1 (+0)