They could add a shoulder strap and make it a very rare item to find

you can actually carry one weapon in your hands (look at it while it is on the ground and select "Put .. in hands") while the other is on your back. You will lose the one in your hands if you disconnect or the server resets tho'. Still, fair enough IMHO.

You can put your secondary weapon onto your back.
Then walk over the other weapon while it lies on the ground. Press Tab and choose "Take weapon in hand" (or something similar)

The problem is that you are actually able to carry two primary guns (mosin+ m4), but i think it is a bug, because you drop the primary (m4) as soon as you switch to your secondary (mosin).

Against it. Already too many weapons in game.

1 Primary.

Bug reports are for reporting bugs. Make suggestions in the Suggestion sub-forum.

If a secondary is allowed in a pack, the weapon should take 20 slots or more.

Although this is the bug reporting forum... I do agree with the suggestion that you should be able to carry two rifles on your back, one on either side of your backpack.

You should be allowed to carry a rifle instead of a melee weapon. I don't see why you couldn't wear a Mosin instead of this heavy fireaxe.

You have to choose what kind of a weapon you want.
I think 1 primary is okay. But the M4 is so good, also for long distance, that you realy need no other weapons. For me, the M4 is to accurately at a distance.
And make a pistol better, if you have a mosin to deffense your self in short distance (or the cutted shotgun)