as you can see in the screenshot I uploaded, I have a Mosin equipped as my primary rifle, and I have the 2nd rifle glitched right under my backpack.
You can only carry the 2nd rifle around like that. Once you take anything in your hands, the 2nd rifle will be dropped, but you [b[can[/b] make a shortcut to the 2nd rifle, and therefore have an advantage of being able to equip 2 rifles simoltaneously.