Pickup guns

Pickup guns, once collected, can be accessed using the number keys 1-6. If you have multiple guns that all stick to the same key, you can pull out the one you want by hitting that key repeatedly.

When your magazine is empty, many of these weapons can be "used" one last time in a spiteful last attempt to slay your enemies. If you just want rid of an empty pickup gun, use your second trigger to drop it.

1
This key brings up your personal gun, the one you picked up aboard your ship. See the Shotgun, Machine gun and Railgun pages for more information. This key also brings up the player's fists if you left the ship without a weapon, or the wrench if you leave your ship without a weapon and then pickup the wrench from the first corpse on level 1.

2
This key holds slight variations on the primary guns that you didn't pick at the start. These guns get used to clobber enemies when they're out of ammo. No special tricks - this shotgun is just a very nice tool for fighting at close range. An accurate machine gun with an extended magazine. Great for putting jellies out of their misery, cutting through floaters and popping open crates - essentially, saving ammo for your more dramatic weapons. This upgraded railgun hits hard and with perfect accuracy. It's great for dropping enemies that like to stay at long range and blast you, like spectres and hostesses, that you'd otherwise have trouble dealing with with your own machine gun or shotgun.
 * Shotgun (10 ammo)
 * Machine gun (50 ammo)
 * Railgun (10 ammo)

3
This key defines more powerful upgrades of whichever primary guns you didn't choose. Again, you can use them as a blunt implement when they're empty. Another excellent choice for handling tough enemies. It's harder to land hits at long range, but it's a great alternative to the fusor for quickly ending the threat from the scarier monsters. Railgunners and shotgunners can use the pickup nailgun to practice with this unique weapon. It has potentially very high damage, as well as being great for handling groups of enemies at medium range. The orbital blast-fusor has even higher damage than the railgun and if you hold it steady it's just as accurate. It will kill almost every enemy in one hit, and is a great option for dealing with rocks, harvesters and other tough monsters that you don't ever want getting too close.
 * Grenade launcher (9 ammo)
 * Dartgun (25 ammo)
 * Fusor (8 ammo)

4
This key is home to several simple but effective weapons. Not quite as accurate or damaging as a railgun, but the pistol does a similar job, doing high damage at medium-long range. It's also fairly common to find. Good for picking off carriers before they start chasing you, and taking out distant spectres in a pinch. When it's empty you can fling it pretty hard! This powerful weapon has a good firing rate, does great damage and is accurate, although the slow-moving plasma bolts are hard to land on moving targets. It's possible to extend your jump with this weapon by firing it against a wall at your feet. It's a fine choice for taking out a group of baddies fast. When it gets empty, you can rip out the ionic regulator and hurl it a few feet in front of you, where it will explode violently a few seconds later. Fires rockets that travel straight and true before exploding with a fearful bang on the first thing they come into contact with. If that thing is alive, it will be horribly wounded by this experience. The fast-flying rockets are a damn sight easier to land than your pickup grenade launcher, and they do a similar job of blasting apart tough enemies. While it can easily kill groups of ordinary baddies, a gun this powerful is kind of wasted on them. It makes a good cudgel when you're out of ammo.
 * Heavy pistol (10 ammo)
 * Plasma gun (20 ammo)
 * Rocket launcher (8 ammo)

5
Some truly special implements of mayhem live under this key. You won't find them on icarus, though. One pull of the trigger will send out an orange energy orb, a second pull will detonate the orb and blast deadly psionic flak into anything nearby. With the right timing you can either wreck the shit of tough baddies or take out an oncoming crowd. A rewarding gun to familiarise yourself with. This gun fires bullets that home in on the nearest baddie. Individually the shots aren't very strong, but they work great against foes with specific weakpoints like carriers, gluttons or spectres. The tracking takes a little while to kick in and the gun doesn't shoot very fast, so be sure to shoot from medium range or further. When it's empty, you can forcibly insert it into an enemy, where it will explode after a few uncomfortable seconds. Launches four of the energy spears used by the smart gun - to either side. Because you'll not be able to deal with anything aggressive that is immediately in front of you, taking out multiple targets in wide-open spaces without having to aim is about the only thing this gun is good for. When it's empty, it will take on a monstrous life of its own and savage several nearby enemies before it explodes.
 * Pulsar gun (10 ammo)
 * Smart gun (25 ammo)
 * Quad tracker (8 ammo)

6
Very strange guns can be selected with the 6 key. They can be found only in the burbs and Athena. A slow-firing exotic weapon that does very high damage and is quite accurate, but harmless to anything beyond close range. It's satisfying, but a little unwieldy. This gimmicky, yet sadistic gun fires compressed air darts that inflate organic enemies until they explode a few seconds later. Mechanical targets won't be affected, and the delayed action makes this one hard to use to defend yourself. Have fun.
 * Airbuster (8 ammo)
 * Inflater (8 ammo)