To start off before making your loadout, think about what enemies are in the level(s) you're speedrunning. Can they fly? Can they attack from a certain range? What kind of damage do they deal? What is their HP in a certain difficulty? Where are their spawn points? Use this idea to think of the loadouts you're gonna set up, along with this guide I've made below.

Note: To quickly switch between weapons, pause the game and get to the settings, where you can choose how the weapon loadout system is shown. I'd recommend "cells" option because you can switch weapons more easily. Additional Note: You don't need to take my recommendations 100% seriously. Using a weapon you're comfortable with, or is very proficient at getting the job done at killing monsters as fast as you can, can speed up the run.

First Step: Speed versus Damage This is often the most intriguing thing to think about for a speedrun. Do you want to move around faster to find the monsters, or do you want to kill them really fast? Think about how you can use this to your advantage over ALL stages. But, some weapons are proficient at both speed and damage, however they either are very expensive, or has a third attribute that lowers the quality of the gun. Additionally, you can make use of the fact that you can have six different weapons on your loadout at one time, while also utilizing the use of stat-buffing armors as well. But in the end, it's about finding the best balance between speed versus damage, dependent on what stage you are in, and what you are comfortable with (this shouldn't really be a problem as a level 27+ will have mastered how to use almost every single weapon type and attribute, combined with a certain armor piece).

Second Step: Reloading Reloading can be a big time loss, especially with certain weapons that can dish out serious damage, but also have a long reloading time (Ex. Automatic Peacemaker).

There is much much more I want to write, but for now, take a highly summarized version. I need to deal with a more important issue about Pixel Gun 3D

2. Find your weapon that you can move around fast, yet deal a ton of damage. One strategy is Weapon-Swapping. This is basically just moving around with a high mobility weapon, then switching to a high damage weapon once you are about to fire upon an enemy. Switch back and forth, and soon it will feel natural to move around.
3. Take note of reloading. Although this can clash with tip #2, think about bosses. If the boss is on low hp, and you need to reload, quickly switch to another gun and shoot, or take a lucky hit with melee weapons.
4. Weak Points/Headshots. Sure, you aim at a monster's weak spot and fire, but this is a speedrun. Try to have a feel of moving around while aiming at a long or short distance, while going for the weak point every time. Practice practice practice.
5. Weapon Choice. Everyone has a preference, but there is one VERY good weapon you might find later on... It is known as The Trapper. If aimed at a bosses' weak spot, it can usually one shot it, except for extreme hp bosses, such as The Bug in the final level. It can go through multiple enemies as well, but since the hitbox is bigger, it is easier to kill multiple enemies. But it can frustratingly hit walls more often.
6. Weapon Choice Variety. Not really necessary, not really confirmed, but you can ignore this, and use the weapons you're MOST comfortable with using. Now, the strategy is to use different weapons that have different traits, yet in the long run deal just the right amount or more damage, while conserving time. Some weapon types you would want are:

• Splash Damage Projectile Weapons (Can help against groups, or even picking off enemies when snipers are just too slow.)
• High Damage Rifle (Basically, a sniper. But most weapons that tend to kill enemies in one shot, like a very strong pistol, or certain Special or Premium weapons can do the job.)
• High damage at close range (While a general machine gun or Automatic Peacemaker may work, certain types of machine pistols can really assist you.)
• Melee: Speed VS Balance (There is the Storm Hammer for Level 27+ that has insane damage and decently high mobility, but it is rather expensive, and requires good timing and skill to use effectively. However, the best weapon that is probably suited to a speedrun while still dishing out high damage is a fully upgraded Dark Force Saber. It has the highest mobility in the game and is incredibly powerful with the right armor, yet very expensive.) If you're looking for a Complete-Speed Melee that's cheap, a Carrot Sword will do, it has an ultra fast swing, but low damage, but has the second highest mobility possible in the game. For complete damage that's cheap-ish, but really fast anyway, you might see a Katana in the future... For groups of enemies, a Magic Orb might help... For damage, just upgrade the Katana. Or Dark Force Saber.