I have noticed that when collecting rounds & shells for shotguns and bolt-action rifles, I would have to repeatedly press F to collect ONE round each, significantly longer than collecting magazines for the rest of the primary and sidearm ammo. I was thinking that collecting rounds & shells can increase with sets of 2 or 3 (buckshot and sniper rounds aren't that big, so grabbing a handfull of individual bullets isn't too ridiculous).
Now I know this suggestion looks like I'm just being lazy pressing F a few more times or just hold F longer to resupply everything all at once, but from a gameplay standpoint, what if you want to keep what you picked up like a rocket launcher or molotovs. If I decide to hold F, then I would loose what I picked up that I want to keep for equipment, and currently there is no control or option to drop weapons. To keep the game going a little bit faster, collecting ammo from ammo caches when using shotguns and bolt-action rifles should be a little faster.