Here is a list of every balance change in my mod scripts and an explanation for why I chose to make that change.

In general, I wanted every weapon to be viable, fun, and unique without straying too far from the vanilla weapon balance. In all honesty, the weapon "tier list" is probably still in the same order for the most part -- but the gap between the best and worst weapons is much smaller now.

Things to note:

• Many numbers are approximate and/or rounded.
  
• DPS stands for damage per second.
  
• DPM stands for damage per magazine.
  
• Accuracy numbers are presented in this order: crouching spread / standing spread / running spread -- smaller numbers are more accurate.
  
• For shotguns specifically, accuracy is written as vertical spread x horizontal spread.

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The assault rifles were already the gold standard for unique, distinctive weapons that don't feel like clones of each other. The problem is that the vanilla AK47 is the best weapon in the game, and it overshadows the other three rifles.

DPS: 424 (was 447) - DPM: 2,200 (was 2,320)
I decided to give the AK47 gentle nerfs, mainly by exaggerating its weaknesses rather than curbing its strengths. I still wanted it to feel useful and powerful, and in my opinion it certainly does.

• 5% less damage (58 > 55)
  
• 20% slower reload (2.4s > 2.9s)
  
• 20% less accuracy (0.5/1/6 > 0.6/1.2/7)

DPS: 410 (was 376) - DPM: 1,800 (was 1,650)
The M16 is neither overpowered nor underpowered, putting it really close to the "Goldilocks Zone." However, I did give it a small damage buff to compete with the AK47 and a small accuracy buff to give it an edge over the SG552.

• 10% more damage (33 > 36)
  
• 10% more accuracy (0.05/0.4/5 > 0.045/0.36/4.5)

DPS: 398 (was 365) - DPM: 2,880 (was 2,640)
The SCAR is arguably the worst assault rifle, mainly because its atrocious reload speed drags down otherwise decent stats. I've buffed the reload speed, damage, and accuracy -- and the SCAR is also indirectly buffed by the reload nerfs of other weapons.

• 10% more damage (single 44 > 48) (burst 132 > 144)
  
• 10% faster reload (3.35s > 3.0s)
  
• 15% more accuracy (0.05/0.35/4 > 0.04/0.3/3.5)

DPS: 436 (was 400) - DPM: 1,800 (was 1,650)
The SG552 shares most of its stats with the M16 in vanilla L4D2, and I mostly kept that in place because I wanted them to keep feeling like "sidegrades." The SG552's scope and higher fire rate are balanced out by having the slowest reload of any assault rifle and less accuracy than the newly buffed M16.

• 10% more damage (33 > 36)
  
• 10% faster reload (3.5s > 3.15s)

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In contrast with the assault rifles, the sniper rifles are atrociously balanced. Some are obviously better than others, and two of the rifles don't feel particularly unique to use either. I've overhauled all of them to feel more distinct and viable.

DPS: 432 (was 360) - DPM: 1,800 (was 1,350)
The vanilla Hunting Rifle is so thoroughly outclassed by its military counterpart it's often considered a Tier 1 weapon in spirit. It has received major buffs to make it a true Tier 2 weapon with a knack for quickly picking off Special Infected. The faster fire rate is addicting!

• 33% larger magazine (15 > 20)
  
• 20% more reserve ammo (150 > 180)
  
• 20% faster fire rate (4/s > 4.8/s)

DPS: 320 (was 360) - DPM: 2,400 (was 2,700)
Also called the Marksman Rifle if you're as cool as I am. This is arguably the second best weapon in the game, so I decided to exaggerate its weaknesses. It's still better than the Hunting Rifle at slaying hordes of Common Infected, but now it's worse against Special Infected.

• 10% less damage (90 > 80)
  
• 10% slower reload (3.35s > 3.7s)
  
• 20% less accuracy (0.05/0.5/5 > 0.06/0.6/6)

DPS: 151 (was 117) - DPM: 1,890 (was 1,575)
The bolt-action sniper rifles are generally considered to be worse than the Tier 1 weapons, so I gave the Scout massive buffs and made it an actual Tier 1 weapon. It will now spawn wherever low tier weapons can be found, and it's great for picking off Spitters and Smokers.

• Downgrade from Tier 2 to Tier 1
  
• 15% less reserve ammo (180 > 150)
  
• 20% more damage (105 > 126)
  
• 10% faster reload (2.9s > 2.6s)
  
• 25% more accuracy (0/0.1/3 > 0/0.075/2.25)
  
• 10% faster fire rate (1.11/s > 1.2/s)

DPS: 266 (was 109) - DPM: 3,795 (was 2,300)
It used to be the worst gun in the game, but the AWP has been given a compelling new role as a Special Infected killing machine. Even without headshots, it can kill Boomers, Spitters, Hunters and Smokers in a single hit. It's still bad against hordes of Common Infected, but now a single bullet does as much damage as a shotgun blast.

• 25% smaller magazine (20 > 15)
  
• 15% less reserve ammo (180 > 150)
  
• 220% more damage (115 > 253)
  
• 15% faster reload (3.65s > 3.1s)
  
• 25% more accuracy (0/0.1/3 > 0/0.075/2.25)
  
• 10% faster fire rate (0.95/s > 1.05/s)

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The shotguns are balanced, but way too similar to each other for my liking. I sought to give them more distinct roles by exaggerating their differences -- now, the Wood and Benelli shotguns are even better at killing Common Infected hordes, and the Chrome and SPAS shotguns are best against Special Infected.

DPS: 1,008 (was 1,012) - DPM: 2,520 (was 2,530)
This weapon was given more pellets in a wider spread without changing the total damage of a single burst. It's even more of a beast at close range than it already was, but past a dozen meters you're out of luck.

• 10% more pellets per shot (11 > 12)
  
• 10% less damage per pellet (single 23 > 21) (burst 253 > 252)
  
• 10% less accuracy (4 x 8.5 > 4.5 x 9.35)

DPS: 1,296 (was 1,008) - DPM: 2,592 (was 2,520)
The SPAS is now a mid-range powerhouse thanks to significantly higher damage and accuracy, but this comes at the cost of a smaller magazine, so it's less effective against hordes. Hard to complain when you're consistently two-shotting Jockeys, though.

• 20% smaller magazine (10 > 8)
  
• 30% more damage per pellet (single 28 > 36) (burst 252 > 324)
  
• 35% more accuracy (3.5 x 8 > 3 x 5)

DPS: 291 (was 288) - DPM: 2,024 (was 2,000)
This pump shotgun was adjusted in the same way as its Benelli autoshotgun counterpart: more pellets in a wider spread, for better and for worse.

• 10% more pellets per shot (10 > 11)
  
• 10% less damage per pellet (single 25 > 23) (burst 250 > 253)
  
• 10% less accuracy (5 x 7.5 > 5.5 x 8.25)

DPS: 368 (was 285) - DPM: 1,920 (was 1,984)
The newer and shinier pump shotgun is the Tier 1 equivalent of the SPAS: a highly accurate Special Infected killer that does worse against hordes due to a smaller magazine.

• 25% smaller magazine (8 > 6)
  
• 30% more damage per pellet (single 31 > 40) (burst 248 > 320)
  
• 10% more accuracy (3 x 5 > 2.5 x 4.5)

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The vanilla SMGs are a bit of a worst case scenario for balance: there's a clear order of best to worst and they're all extremely similar to each other. I decided to make them much more unique by taking cues from the design of the assault rifles.

DPS: 320 - DPM: 1,200 (was 1,000)
The Uzi has been adjusted to be similar to the SCAR: a highly accurate weapon with a huge magazine, balanced out by relatively low damage and a slow reload.

• 20% larger magazine (50 > 60)
  
• 25% slower reload (2.2s > 2.75s)
  
• 30% more crouching accuracy (0.7 > 0.5)

DPS: 384 (was 400) - DPM: 1,200 (was 1,250)
In vanilla L4D2, this SMG outclassed the others with its absurd DPS and no significant downsides. I've gently nerfed it to be in line with its siblings, making it the Tier 1 M16 equivalent.

• 5% less damage (25 > 24)
  
• 33% less accuracy (0.85/1.2/3 > 1/1.5/4)

DPS: 400 (was 347) - DPM: 1,350 (was 1,300)
The MP5 was reimagined in the style of the AK47: higher damage, lower capacity. It's now the only SMG that kills Common Infected in two bullets instead of three. Its reload speed was also buffed, but it's still the slowest of the SMGs.

• 10% smaller magazine (50 > 45)
  
• 15% more damage (26 > 30)
  
• 10% faster reload (3.1s > 2.8s)
  
• 15% less accuracy (0.75/1.1/3 > 0.85/1.25/3.5)

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The secondary weapons are all very unique, but again, there's an obvious hierarchy in viability. There's only so much I can do with my scripting skills, but I've tried to make every secondary option a compelling choice.

DPS: 198 single, 396 double (was 166, 331) - DPM: 688, 1,376 (was 540, 1,080)
The Pistols are often considered some of the worst weapons in the game, being thoroughly outclassed by melee weapons up close and the Magnum at a distance. I've given them major buffs so going guns akimbo feels as cool as it should be.

• Removed accuracy penalty when incapacitated
  
• 5% larger magazine (15 > 16)
  
• 20% more damage (36 > 43)
  
• 25% more standing accuracy (1.5 > 1.125)

DPS: 293 (was 267) - DPM: 616 (was 640)
I've heard people say the Magnum is even better than some of the primary weapons in the game, so something had to change. I gave it several nerfs, including a 7-shot magazine -- but it also received a damage buff as compensation so it can still kill a Charger without reloading.

• 15% smaller magazine (8 > 7)
  
• 10% more damage (80 > 88)
  
• 30% less accuracy (0.5/1.25/3 > 0.66/1.6/3.9)

There's unfortunately not much I can do to change the melee weapons with a simple script, but I decided to give sharp melees a slight nerf and blunt melees a slight buff just to even things out a bit.

• Sharp melee friendly fire damage raised to 10 on Expert
  
• Blunt melee friendly fire damage lowered to 5 on Expert

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The cruel irony of Left 4 Dead 2 is that the heavy "Tier 3" weapons are generally worse than standard primaries despite their rarity. I've adjusted all of them to be worth using so players will actually be excited to find them.

DPS: 168 (was 100) - DPM: 400
This hunk of junk has had its reload speed nearly cut in half so it's actually an effective weapon. It's very fun to use now, if you can believe that!

• 40% faster reload (4s > 2.4s)

DPS: 455 - DPM: 10,000 (was 7,500)
The M60 was already a good weapon, but it runs out of bullets too quickly to justify picking it up sometimes. I've increased its magazine size and lowered its accuracy to make it the "Rambo" weapon of choice.

• 33% larger magazine (150 > 200)
  
• 25% less accuracy (0.5/1/6 > 0.625/1.25/7.5)

Due to what is almost certainly a typo, the Minigun has a cooldown time of 3 seconds when it overheats. This has been increased to a much more reasonable 20 seconds.

• 667% longer cooldown (3s > 20s)

This heavy turret has an absurdly long cooldown time in vanilla L4D2, so I cut it in half to encourage more players to try this thing out. Note that the cooldown is intentionally slower than the Minigun's because this turret does more damage.

• 50% shorter cooldown (60s > 30s)

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I also made some miscellaneous changes to things that are not weapons. I would have done a lot more (nerfing the Bile Jar, for instance) but there's only so much you can change in the game's code, unfortunately.

As much as I love Adrenaline, I have to admit that 90% of the time, the speed boost is too niche to make up for the paltry amount of health it provides. Therefore, I increased Adrenaline's health boost to 30 so it's a more compelling choice compared to the Pain Pills.

• 20% more health restored (25 > 30)

Molotovs are better at killing zombies and Bile Jars are better at distracting them, leaving the Pipe Bomb without a niche as the weakest throwable item. I decided to simultaneously buff its killing and distracting potential by increasing the fuse/beep time to 8 seconds.

• 33% longer fuse time (6s > 8s)