It's instanly noticeable that meele weapons have a "dash" while swinging, but some long range guns also have a hidden buff that is not that noticable at first. In this guide I'll cover some cases that I noticed so far

Let's start with the most noticable gun: KesoWhile equipped it gives a strong speed boost and increased jump height even with an empty mag.
That's about it, no "dash" or recoil as far as I know, so it's pretty easy to use in most situaions.

Bukanee has two intertwined mechanics that compliment eachother: recoil and disabled gravity.
When shooting Bukanee player will not be affected by gravity and will be pushed by the recoil of the gun.
It's important to note that the recoil is not what's pushing the player against gravity as you can easily move in the direction you shooting while aiming horizontally and not fall(just try it it's hard to explain)

FG42 has an interesting effect on walljumping. When walljumping with no weapon or most other weapons the walljump will have mostly just horizontal momentum added so it is not very effective in gaining height. But when FG42 is equipped, walljump will be just as high as normal jump from the ground, allowing to reach otherwise inaccesible locations

HK_G11 has the same effect but also a little bonus ability: 2(two)(!!) walljumps in a row, wich when paired with increased vertical mobility mantioned previously opens up a lot of spots on the map

It does not seem to be a bug as it is often placed in places requiring a lot of mobility and only affects theese two three weapons(afaik)

Katana also affects walljumps quite a bit. You can scale a lot of walls by using m2+m1 dash and spamming jump while walking into the wall. Proper timing of dash can allow to go around leges on walls.
Basically HK_G11 but with 3(i think) walljumps instead of just 2 and also a meele with a very good dash. Not as fast or insane as Nizeh, but makes you feel like a ninja kinda guy!

Bayshore gives a speed boost, 15(i think) walljumps and increases jump height.
It was made specifically for high speed encounters and not usual fights so it's not as overpowered as it seems.

You can slow down by leaning(Q or E) in air

That's all I managed to recall and/or find so feel free to suggest smth in the comments. Actually it would be much easier if you just rewrite this guide yourself, 'cus I don't wanna do it.
Also it's my first time writing a guide that's why it looks so plain and hard to read, sorry.
anyway hope this helps have a good day bye