Early game strategies for D-class/Scientists to acquire a gun ASAP.
How to Fast Gun Start
Assessing Your Location
First thing to do immediately after spawning is to find out what map generation LCZ is.
As D-class this can be done immediately after leaving your cell room & after going through a few hallways. As a scientist however this can be more complex. Scientists spawn at a random important room. This can be a checkpoint, 012, GR room, WCs, and even 914 in some occasions. Always check behind you when you spawn as a scientist.
A few ways to determine the map layout, is by looking out for how hallways are lined out. If there's a lot of corners it may be heart or arms. If it continually going straight it may be line or loop.
You can also determine the layout based off of important rooms & how they are positioned.
After you've found out the map layout it's time to find a gun!
Choosing a Strategy
There are two main strategies that may vary based on the situation (How early SCPs/guards arrive, someone has already taken the pistol/looted armoury, etc). If it is the very start of the game, it can be worth while to hunt for the pistol along with finding a keycard (If D-class). If scientist however unless you haven't located 914 & armoury yet, this strategy is risky & most likely will waste your time.
Rooms where pistol can spawn: 012, WCs (Men's side), GR room (Inside of the containment room), and 173's (PT) room (Door at the top of the staircase leading into a small security room). There is also an additional one in the armoury which can be useful if you haven't found a flashlight yet.
The second strategy is to instead rush to armoury. To do this you'll require a keycard to access 914 which you'll need to upgrade said card to a sufficient level to open armoury. Fastest way to do this would be to use 1:1 to get a guard keycard. 2 times through 1:1 with a scientist/janitor keycard, 1 time with a zone manager or major scientist keycard.
After obtaining your guard keycard or better, it's time to find the armoury. If you know the layout of the map this should be relatively simple, and you may have come across it already while searching for the pistol/keycard/914. The room in particular is marked by ##.
Worst case scenario: Pistol & armoury already looted & SCPs are in LCZ. In this situation there's still hope! But by the time you get your weapon, if at all, it will definitely be midgame in the round. You'll have to bide your time hiding from SCPs & search every corpse you come across. However, by this point, it'll be much better to just find a keycard that can open checkpoint ASAP & start your search in HCZ instead (Or try to escape).
By this point you've either obtained the pistol, or started to loot armoury. If you're particularly lucky you can easily achieve this before anyone has found 914, or while everyone is still upgrading their cards. With a weapon everyone else is at your mercy, and you can defend yourself against MTF/chaos. In general I'd advise to always aim for getting a weapon before leaving LCZ unless SCPs/guards have started to roam the zone.
When upgrading in 914 do not bother locking the gate. This may sound strange at first, but by doing this you are trapping yourself in if an SCP finds it. If there is no one else in 914, or people you can trust, it is far better to put your card in the intake before activating the machine, and then sitting in the corner outside of the gate. This way, if an SCP or other threat enters the room, they'll most likely walk straight into 914 while you can run away to safety.
Another thing to note: Never upgrade your guns unless you have ammo for them or know you can get ammo for them. If you upgrade your P90 to an epsilon-11, you'll have one full magazine, and no spare ammo. Much better to just take the P90 with 2 extra mags from armoury.