First Half

Cossak 3 is an autoscroller, so there isn't much to explain that isn't in the videos. There are a few notes though.

First, very simply, the screen does not begin scrolling until you move to the right past the spawn point. (?)

The only real thing to note, is to shoot the 4 turrets when they spawn to avoid lag-generating bullets. After the destroying the fourth turret, you can switch to a weapon to refill, and then (if necessary) to Ring before the next screen.

On the screen between the long screens, use Ring to destroy the saws on the platforms, bot for its effectiveness and very low ammo usage.

On Weapon Refills

The current WR route only collects a weapon drop for Ring in the first half. Note the WR route is extremely tight on ammo usage, rightfully so since collecting ammo and pausing to switch weapons to refill different weapons takes several seconds.

If you are not looking for a WR, collecting the first refill with Dust equipped makes sense. Just remember this takes time.