Guns like the AVS-36, SVT-38, SVT-40, AKT-40, and AVT-40 can be loaded with mosin stripper clips.
Also if you walk over a weapon that uses the same ammo as your gun you should get it.
Example: You have an SVT-38 and walk over a mosin, you should pick up its ammo as stripper clips or loose rounds.
Ammo scarcity is an intentional design choice by the Devs. It both promotes grinding (or paying) to get ammo pouches, and discourages camping / conservative playstyle. The general leitmotiv of the game is to encourage rushing, with little consequences for dying and incentive to frequent squads turnover.
It encourages camping. You only need 1 engineer in a squad and you have unlimited ammo right at the spot you camp. But if you attack and especially without rally close by. By the time you reach objective you are out of ammo.
IF you are far-seeing enough to put an engineer in each squad, and you have upgraded your squads to allow one in the first place.
Anyway, it’s only one of the camping-adverse aspects. Players sooner or later realize that rushing points and fighting close and personal nets significantly more XP than sniping from afar.
You cannot even use ammo from your secondary weapon for your primary weapon, even when those are actually the same weapon. E.g. for some snipers I have the same rifle without scope as a secondary weapon, but I cannot exchange ammo between them.
But this is acceptable, because it discourages camping, as said by others.
Yes, and furthermore that would nullify the need for large ammo pouches.
Ammo is in a really weird spot: even if you’re run out of ammo with your Mosin, go pick up another Mosin from a dead friendly, you can’t use the ammo boxes you’d built as it’s considered “someone else’s gun”. Sorry what?
That’s in all likelihood to avoid the risk of people skipping the grind by playing professional scavengers.
Otherwise, it could even degenerate into some guys deliberately trying to get their high-level teammates killed to steal their weapons (and we all know there would be someone who would do that).
I mean, at least for the weapon you spawned with (Mosin), you should be able to replenish your ammo even if you picked it up from a teammate. (in other words, for weapons you’ve unlocked)
You can’t do that even for your own weapon if you drop it and then pickup.
At the same time, mosin rifle with scope and regular mosin rifle have the same ammo. So inf from the same squad can pick up mosin with scope and have full ammo count. Not sure if that is applied to other rifles, like semi-autos.