Good backpack/sustainment pack for an assistant M240 gunner

As the title says im looking for some type of backpack to store my ammo in. My usual combat load would be about two 250 round belts of ammo, and usually dont need to carry this ammo for longer than a few kilometers, as such neither the comfort or the size have to limit your reccomendations. As such i have been looking at MAP's such as the Twinneedle MiniMAP and the Platatac Mini Alpha Assault Pack and wanted to learn if anyody knows if that those kind of packs are viable for what i want to achive or if i need to find something bigger or just another brand.