The do's, the don't's, the general philosophy, and the builds. Don't be that guy who runs ahead and gets leeched.
How to Be High-Flying Scout
You don't actually scout. Running off ahead of your team leads to dying in inconvenient places. Instead you light up inconvenient caverns, take out inconvenient enemies, and grab inconvenient minerals. Things that are easy for you will be hard for the rest of your team, and vice-versa. An important part of being Scout is knowing what to do by yourself and what to leave for teammates.
This mostly comes from experience, but broadly: if it glows or it's on the ceiling, shoot it. If you can't see the ceiling in a new cavern, light it up. If a mineral deposit is high up on a wall, grab it. If a teammate is grabbed, rescue them. Don't occupy yourself killing Swarmers or mining ground-level deposits if there's anything better to do. This also means that as you become more skilled and trust in your team, you should build in ways that accentuate your strengths even if they exacerbate your weaknesses.
Lastly, you have incredible clutch potential if you play carefully. Most enemies don't have ranged attacks, so your ability to create distance is an extremely potent defensive tool, which can keep you alive even with all teammates downed.
Note: All weapon information is accurate to Hazard 4 and 5.
The M1000 and Deepcore GK2 are both very solid weapons with similar niches. They both excel at mid- to long-range single-target damage, but while the M1000 has perfect accuracy natively and can afford to build for damage, the GK2 has to build to compensate for its baseline inaccuracy and recoil. They also both suffer from painful reloads. As a base weapon I find the M1000 to be stronger, but the GK2 has better Overclocks which can help it to compete.
The GK2 has a very simple playstyle regardless of build: shoot weakpoints. There really are no subtleties about this gun. It has more of a mid-range focus than the M1000 and is noticeably more ammo-hungry. I consider this to be a generalist weapon; it mitigates the Scout's usual weaknesses but blunts their inherent strengths. As a result, it's well-suited for solo play but has less to offer in a coordinated team.
In the past, the GK2 was often built to reach 15 damage to one-shot Swarmers. With the new Thorns perk, I don't think this is necessary anymore. An accuracy-focused build like 12113 is generally better in most situations, since it allows for more reliable weakpoint hits at mid-range and is better at dealing with ceiling-crawlers. Reloading is the bane of the GK2's DPS, so I consider the Gas Rerouting and Compact Clips Overclocks to be very strong. AI Stability Engine is also intriguing, giving the gun perfect accuracy and freeing up modifications for more damage.
The M1000 is more complex. Holding down the trigger will charge a shot; charged shots consume 2 bullets and deal double damage (or more) with perfect accuracy. It's tempting to use charged shots exclusively, but if you can finish an enemy off with an uncharged shot, you should. Using uncharged shots when appropriate will increase your effective DPS, stretch your ammo, and minimize reloading.
Increasing the M1000's damage is essential. I enjoy the 21123 loadout, with the first two mods being non-negotiable. This allows the M1000 to kill Grunts on a charged bodyshot or uncharged headshot, which helps immensely with clearing out waves. Unfortunately, the M1000's Overclocks are generally bad. Minimal Clips is the only one I can recommend; more ammo and faster reloads are always nice.
The Scout's primary weapons are both respectable, but the choice of secondary weapon is hardly a choice at all. They both have the gimmick of being short-ranged weapons on a class that usually wants to stay far away. The Jury-Rigged Boomstick is stronger and less awkward than the Zhukov NUK17s, and boasts better Overclocks to boot. The only niche I've found for the Zhukovs' ammo-burning sustained DPS is in getting speed-kills on Dreadnoughts, but even that is a little shaky.
The Boomstick can be built for either ammo or raw damage, depending on how often you want to use it. Regardless, I strongly recommend X2XX1. Being able to dump both barrels in a fraction of a second, then swap back to your primary and let the Boomsticks passively reload, is incredibly valuable. Rather than choosing between using your primary and secondary, you can weave them together in sustained combat for higher DPS.
For Overclocks, Stuffed Shells is the strongest generalist with Jumbo Shells being a more extreme ammo-guzzling alternative. But in my opinion, the best Boomstick Overclock by far is the Special Powder. This OC makes your shots act like a directional double-jump when you're airborne, allowing you to cancel fall damage even when your grappling hook is on cooldown- an incredible boon to getting those risky mineral deposits.
Compared to the Boomstick's ability to seamlessly interlace with your primary, the Zhukovs are demanding and fussy. They offer sustained DPS as opposed to the Boomstick's burst, but guzzle ammo too quickly to be used continuously. Their continuous damage also demands that you stay at short range for longer than the Boomstick does, which is a dangerous proposition for a class whose best defense is running away.
All of this adds up to a weapon that's only suited for shredding a big enemy up close that won't fight back. Dreadnoughts happen to fit the bill. 22121 is the best loadout here; combined with an IFG for the damage synergy, you can melt a Dreadnought's healthbar in seconds. Even then, I'm not certain that the Zhukovs are carrying their weight- your primary weapon could do almost as well.
The Scout's grenades are all non-damaging crowd control. The Pheromone Canister and Cryo Grenade are significantly more disruptive than the IFG's soft slowing CC, but you can carry 6 IFGs as compared to 4 of the others. IFGs also increase enemies' vulnerability to damage by 30%, which makes them strong if used proactively. However, they're a poor panic button: If an enemy can be neutralized by outrunning it, the Scout isn't threatened in the first place.
Pheromone Canisters cause enemy infighting; other bugs will attack anything painted by the grenade, and painted enemies will retaliate, which can swiftly embroil an entire wave in civil war. This is quite strong on higher difficulties where more enemies will spawn. The effect lasts for up to 10 seconds; enemies will rarely be able to kill each other outright in this time, but you or your teammates can mop up the clustered and weakened bugs with little trouble.
Cryo Grenades have the most immediate effect; most enemies will be immediately frozen in place with one grenade, killing fliers and negating on-death effects. Larger enemies will thaw more quickly, and Bulk Detonators require two applications. While frozen, enemies take massive damage even on body parts that are normally armored; it's possible to freeze and instantly kill an Oppressor with the Boomstick. Unfortunately, they're unreliable in the Glacial Strata and around teammates using fire-based weapons. Definitely consider these for armored enemies if your team lacks a Driller.
Epilogue: The Flying Foothold
Advanced technique, use responsibly.
I consider this the most important Scout tech, though it's risky unless you have a way to cancel fall damage while your grappling hook is on cooldown. It's useful whenever you have to mine minerals high up on a sheer wall and don't have an Engineer to create platforms for you.
Grapple towards the wall and hold forwards, but release the grapple right before you reach the wall and power-attack it. If done correctly, your power attack should carve out a small hole in the rock, which your remaining momentum from the grapple will carry you into!
This is an extremely powerful trick, but never attempt it if you're scared of fall damage- the random shape of the hole means that it's never 100% reliable even with perfect technique.