As it stands the new method of loading bullets into your mosin requires one of your left hand fingers to hold a quickslot key. As your three fingers, ring finger, middle and index rest on the wad keys respectively it makes it difficult for all axis movement when you require your finger to be holding one of the number keys.

For me and i suppose for many others the first 1-2 quickslot keys are pressed using your ring finger whilst 3-9 are index. My suggestion is to instead just hold down the key bringing up the same prompt that loading bullets into mag gives and then load bullets by holding Left mouse button. This then allows for free movement and natural mouse movement. Same applies for shotguns or just chambering loop in general.

Thank you :)