I'm not sure if this has been mentioned before, I searched for it and didn't find anything but apologies if it has.
I noticed an issue with the magazine for the MK17. I'm playing on Xbox One and after unlocking the MK17 I went to customise it. I only have the 20rnd mag for it and changed the colour to black. In the Gunsmith it displays correctly, however in the Loadout it displays the 30rnd mag in the default colour. In-game it also displays as a 30rnd mag in the default colour but the actual ammo count is 20. I wasn't sure if this was related to my save file so I started a new save and found it to be the same.
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Spoiler: Show