Ammo packs and secondary weapons

DO weapons in the primary and secondary slot share ammo if they are the same?

I’m trying to figure out of I get more out if unlock the secondary or backpack slot is better. Will I hold more ammo if say I give a sniper two of the same rifles or if I give him one and an ammo pounch?

Yeah they share ammo if they are the same type.

Small ammo pouch gives you 10% more ammo.
Large ammo pouch gives you 100% more ammo.

If you just want more ammo the secondary might be the best but then you will lack the versatility that backpack gives you.

Can you pick up weapons if you don’t have the secondary slot open?

yes you can. but picking up weapons is a bit buggy right now

What else can you put in a backpack apart from medkit?

That’s not the backpack slot. The backpack slot is up next to the sidearm slot. You can put ammo packs, grenade pouches and backpacks in it. Grenade pouches let you carry multiple grenades and backpacks let you carry multiple medkits or toolkits.