Here’s some formula to calculate the accuracy and firing rate of guns, or you can skip to the conclusion part at the bottom
Calculating total dispersion:
-> {0 ~ 45} means a random number between 0 and 45
Total_dispersion =
- {0~[45 x (10- skill level of the type of gun you are firing)]}
- {0~[15 x (10- level of marksmanship)]}
- {0~[15 x (12-Dexterity)]}
- {0~[15 x (12-Perception)]}
- {0~[30 x (Encumbrance of left arm +Encumbrance of right arm)]}
- [0~(60 x encumbrance of eyes)]
- (0~dispersion of the bullet)
- (0~dispersion of the gun)
- {(total recoil/4)~total recoil}
If you have targeting system CBM, total dispersion = total dispersion x 75%
If you are firing a gun that is not designed for under water usage under water, total dispersion = total dispersion x 4
If distance between you and target < volume of gun/3 , (except you are firing a shotgun)
total dispersion = total dispersion x [ (volume of gun/3) / distance between you and target ]
If you are firing a rifle, and the distance between you and target > 10,
total dispersion = total dispersion x [1 - 0.4 x (distance to target- 10) / distance to target]
missed_by = total_dispersion x 0.00021666666666666666 x distance between you and target
If missed_by > 1, you missed
hit_value = (missed_by - 0.5) ~ (missed_by + 0.5)
hit_value < 0.4= hit torso
hit_value > 0.4=1/4 chance hit the legs, 3/4 chance hit the arms
goodhit = missed_by / max(Speed of target/80, 1.0)
goodhit <0.1 = headshot
goodhit < 0.1-0.2 = critical
goodhit < 0.2-0.4 = a precise hit
goodhit < 0.4-0.6 = hit
goodhit < 0.6-0.8 = graze
goodhit > 0.8 = missed,
Deal with recoil:
recoil a shot added to total recoil = recoil of the gun - {strength x 7 ~ strength x 15} - {0 ~ marksmanship x 7}
When firing at burst or automatic, the recoil of shots after first shot are halved
The total recoil is halved each turn, marksmanship and strength helps
The lowest total recoil without aiming is 150
How does aiming works?
a scope has two properties: aiming speed and aiming dispersion
a scope only works when total recoil > aiming dispersion
When there are many scopes available, the one with lowest aiming speed is used (the lower the aiming speed the better)
Aiming decrease total recoil, aiming speed, marksmanship skill, skill of the type of gun you are firing, and dexterity have impact on how much total recoil is reduced
Things about fire rate:
Well, all guns have a property called “fire rate”, but it has no impact on how fast a weapon can fire, different types of gun has different formula to calculate fire rate:
Handgun: When handgun skill > 6, each shot take 10 AP, if <6, it takes = 80- (10 x handgun skill)
Shotgun: When Shotgun skill > 3, each shot take 70 AP, if <3, it takes = 150- (10 x shotgun skill)
SMGs: When SMG skill > 5, each shot take 20 AP, if <5, it takes = 80- (10 x SMG skill)
Rifle: When Rifle skill > 8, each shot take 30 AP, if <8, it takes = 150- (10 x rifle skill)
Bows: When Archery skill > 8, each shot take 20 AP, if <8, it takes = 220- (10 x archery skill)
Throwing: When throwing skill > 6, each shot take 50 AP, if <6, it takes = 220- (10 x throwing skill)
Launchers: When handgun skill > 8, each shot take 30 AP, if <8, it takes = 200- (10 x launcher skill)
When you fire at burst or automatic, it takes THE SAME TIME as fire a single shot, and if the target is dead, you will automatically aim another mob within 4 blocks of the previous target
CONCLUSION:
Fire rate and accuracy determines how much damage you can deal to zombies,
to be accurate:
- Make sure encumbrance of eyes and arms are about 0
- Make sure total recoil is very low, walk to decrease the total recoil to a reasonable number before use scopes, use scope with lowest aiming speed
- level up your marksmanship skill and specialized skill for the type of gun you use
- Importance of strength > dexterity = perception
- The effect factors have on accuracy: Encumbrance > total recoil > specialized skill > marksmanship > dispersion of gun&ammo
- Fire at zombies that are close to you (not too close)
- aiming system is super helpful!
to increase fire rate:
- Choose guns that can fire in burst or automatic mode (I use MP5 and G3 in the past, they are good for early game, pneumatic assault rifle is great once you can craft it), never fire single shots (bows are not considered as guns)
- Fire at a group of zombie is a good idea
I am not a native English speaker so if there are grammar problems or something you don’t understand please point it out 
Wish this can help you