Of course every gun is going to be map and situation dependent however, this will serve as a general guide to get you started.
Number 5 the Mosin-nagant
The mosin is a powerful bolt action rifle. Early in the wipe you will be able to down any PMCs or scavs in just a few shots. Its recommended to try and keep your engagements at medium to long range when rocking the mosin. You can also upgrade the mosin by adding a scope, shortening the barrel or adding different grips. If you're going to use the mosin after the start of the wipe then I highly recommend that you add a scope as soon as possible. This will give you a huge advantage over other PMCs at long range. You don't get to kill players in a few shots without some draw backs. The slow rate of fire will put you at a huge disadvantage when inside of a building. If you end up in a close combat encounter then you really need to aim for the head and make your shots count. Reloading the mosin takes forever. I highly recommend going into raid with a side arm if you decide to use any bolt action rifle. Which is why the mosin is only taking our number 5 spot.
You can buy the mosin from level 1 Prapr for just 35,000 rubles.