A weapon's bullet cost determines its starting ammunition, maximum ammunition (when combined with magazine size), and how much ammunition it receives from using an Ammunition Pack.
How ammunition works in GTFO[]
At first, the ammopack appears to behave rather inconsistently, filling up different weapons by different amounts, and sometimes giving an extra bullet (or not). This is a byproduct of the way that ammunition works in GTFO.
Ammunition works on a bullet cost system, and every single weapon has its own defined bullet cost. For ease of reading, this article shall measure them in terms of units (easier to write that way).
Prisoners can carry up to 460 units of ammunition in reserve for main weapons, but only 230 units of ammunition in reserve for special weapons, and 150 units of tool ammo. Ammo in the weapon's magazine does not count towards this limit - therefore, prisoners are always encouraged to reload when resupplying, to avoid wasting a resupply. To explain this in form of an equation:
The amount of bullets a prisoner has in reserve is calculated via dividing their current reserve units by the weapon's bullet cost, and then rounding down, like so:
Prisoners will start missions with exactly 300 units of primary ammo (in total), 150 units of secondary ammo (in total), and 100 units of tool ammo - (the only exception to this being during Training and R7C3, where prisoners are sent in with nothing). The magazines of the weapons will be filled with ammo from this pool, so the reserve pool will initially contain less ammo than the advertised starting capacity (so, in the case of the Pistol: bullets, then with we get starting magazine/reserve is 15/85 (and units in reserve - with space for another 235 units)).
Reloading a weapon subtracts units of ammo from the reserve. Tools don't reload.
The bullet costs of many weapons in GTFO aren't integers, and neither is the count of ammo units currently held by a prisoner - but, of course, one cannot load a weapon with half of a bullet (at least in GTFO). Hence why bullet counts are always rounded down. For example, if a prisoner has a full units of ammo in reserve for their Sniper - the sniper's (pre-ALT://R4) bullet cost of 25 means that the prisoner has bullets in reserve. And as that last of a bullet is rather useless, the prisoner only has 9 bullets. However, if the player then exhausts their ammunition supply (by using those 9 bullets, or, rather, 225 full units of ammunition), the prisoner will still have those lingering 5 units of ammunition in their reserve - which can then potentially be used later on upon resupplying enough to turn that partial bullet into a full bullet.
So, what exactly does the ammopack do?[]
The ammopack provides units of ammunition to the reserve ammunition capacities of a player's primary and secondary weapon. If resupplying would cause the primary to have more than 460 units in reserve or the secondary to have more than 230 units in reserve, the reserve quantities would be capped at 460/230 units respectively.
Magazine capacity does not count towards this cap, but ammopacks do not refill the weapon's magazine. Therefore, to get maximum value from an ammopack, prisoners must ensure that they fully reload their weapons, to ensure that as much space as possible will be free in reserve.
And if prisoners really wish to maximize bang for their buck with ammopacks, they may wish to refrain from fully refilling their weapons, unless they have space in their reserve ammunition for the full 90 units of ammo.
What about Tool Refill packs?[]
Tool Refill Packs replenish units of tool ammunition to your equipped tool (bear in mind the total tool ammo capacity of 150 units) - in other words, it provides exactly 20% tool ammo (but all tools besides the C-Foam Launcher do not have a bullet cost which cleanly divides by 150, 30, and 100).
Also, on the topic of tools - Sentry Guns internally have a bullet cost multiplier of 0.285 (effectively having 526.315789474 total units of sentry ammo, starting expeditions with 350.877192982 units, tool refill packs replenishing 105.263157895 units) - but this bit of internal multiplication is only of interest when looking into the raw stats behind the sentries and trying to make sense of them - and is of very little practical use.
And, of course, the Biotracker does not use ammo in any way, shape, or form.
Sidenote: the awkward numbers, and implications for optimal ammopack usage[]
You may have noticed that pretty much every single weapon (barring the Scattergun) has a total ammo capacity which isn't neatly divisible by its magazine size. You may also have noticed that very few weapons have a bullet cost which is a factor of 90 (resupply amount), 460 (primary unit limit), or 230 (secondary unit limit). And, of course, that 90 isn't a factor of 230 (or 460), and that 150 isn't a factor of 230 (likewise for 300 and 460).
All of this ultimately suggests that these numbers are intentionally awkward, to contribute to GTFO's overall vibe of making players feel underequipped (knowing that full ammo leaves you with a partial reload means that players may not feel confident about their supposedly 'full' ammo reserve) and rather powerless (not entirely feasible for players to assert control by fully optimizing ammopack usage without leaving themselves far from their full ammo capacity), and the fact that this bullet cost system is completely hidden from players leaves lingering uncertainty about the effectiveness of resupplies (even after a player (such as yourself) learns about it).
Ultimately, attempting to fully optimize ammopack usage is a fool's errand (unless, of course, one is prepared to do quite a lot of maths when deciding whether or not to resupply), leaving players who are seeking to optimize it mostly reliant on heuristics.
However, as the overall unit capacities of special weapons are half as much as that of main weapons, but both special and main weapons gain 90 units of ammunition per resupply, prisoners are advised to use 2 units of special ammo from their special reserve for every 1 unit of main ammo they use from their main reserve once both weapons have similar amounts of reserve ammo, to ensure that both weapons can always get roughly the same amount of ammo back from a resupply (minimizing wastage caused by overfilling either weapon).
Refill Amounts (rough amounts)[]
Please note the data shown below was not datamined - it was collected in-game by emptying all weapons so they had 0% ammo (but not necessarily 0 units of ammo) then using the Ammo Refill Pack (and reloaded) until they reached 100% ammo. The article pages for the (non-removed) weapons contain the exact resupply amounts (non-rounded), along with their bullet costs - alternatively, check out u/RaybanYoda's complete GTFO weapon data spreadsheet
Weapon | First ammo pack use | Second | Third | Fourth | Fifth | Sixth |
---|---|---|---|---|---|---|
Shelling S49 Pistol | 18%
30 Total Bullets |
36%
60 Total Bullets |
54%
90 Total Bullets |
71%
120 Total Bullets |
89%
150 Total Bullets |
100%
168 Total Bullets |
TR22 Hanaway DMR | 18%
16 Total Bullets |
35%
31 Total Bullets |
52%
46 Total Bullets |
69%
61 Total Bullets |
87%
77 Total Bullets |
100%
89 Total Bullets |
Malatack LX Assault Rifle | 18%
61 Total Bullets |
36%
122 Total Bullets |
54%
183 Total Bullets |
71%
244 Total Bullets |
89%
306 Total Bullets |
100%
342 Total Bullets |
Van Auken LTC5 SMG | 18%
70 Total Bullets |
35%
139 Total Bullets |
53%
208 Total Bullets |
70%
277 Total Bullets |
88%
346 Total Bullets |
100%
393 Total Bullets |
Accrat Golok DA Bullpup Rifle | 17%
60 Total Bullets |
35%
120 Total Bullets |
52%
180 Total Bullets |
69%
240 Total Bullets |
87%
300 Total Bullets |
100%
346 Bullets |
Drekker Pres MOD 556 Rifle | 17%
22 Total Bullets |
34%
44 Total Bullets |
52%
66 Total Bullets |
68%
87 Total Bullets |
85%
109 Bullets |
100%
128 Bullets |
Raptus Steigro HEL Autopistol | 18%
112 Total Bullets |
35%
225 Total Bullets |
53%
337 Total Bullets |
71%
450 Total Bullets |
89%
562 Bullets |
100%
635 Bullets |
Van Auken CAB F4 Carbine | 17%
64 Total Bullets |
34%
128 Total Bullets |
51%
193 Total Bullets |
68%
257 Total Bullets |
85%
321 Total Bullets |
100%
376 Total Bullets |
Bataldo 3RB HEL Revolver | 18%
18 Total Bullets |
36%
36 Total Bullets |
54%
54 Total Bullets |
72%
72 Total Bullets |
90%
90 Total Bullets |
100%
100 Total Bullets |
Raptus Treffen 2 Machine Pistol | 18%
95 Total Bullets |
36%
190 Total Bullets |
53%
285 Total Bullets |
71%
379 Total Bullets |
89%
474 Total Bullets |
100%
543 Total Bullets |
Accrat ND6 Heavy SMG | 18%
60 Total Bullets |
36%
120 Total Bullets |
54%
180 Total Bullets |
73%
240 Total Bullets |
91%
300 Total Bullets |
100%
331 Total Bullets |
Hanaway PSB Double Tap Rifle | 18%
24 Total Bullets |
36%
48 Total Bullets |
53%
72 Total Bullets |
70%
95 Total Bullets |
88%
119 Total Bullets |
100%
135 Total Bullets |
Malatack CH 4 Burst Rifle | 17%
51 Total Bullets |
35%
103 Total Bullets |
53%
174 Total Bullets |
71%
206 Total Bullets |
88%
257 Total Bullets |
100%
292 Total Bullets |
Buckland SBS III Sawed-off Shotgun | 18%
8 Total Shells |
36%
16 Total Shells |
55%
24 Total Shells |
75%
33 Total Shells |
93%
41 Total Shells |
100%
44 Total Shells |
Accrat STB PDW | 18%
69 Total Bullets |
36%
139 Total Bullets |
54%
208 Total Bullets |
72%
277 Total Bullets |
90%
346 Total Bullets |
100%
385 Total Bullets |
Bataldo J 300 HEL Shotgun | 16%
16 Total Shells |
34%
33 Total Shells |
51%
49 Total Shells |
68%
66 Total Shells |
85%
82 Total Shells |
100%
97 Total Shells |
Weapon | First ammo pack use | Second | Third | Fourth |
---|---|---|---|---|
Buckland S870 Shotgun | 29%
8 Total Shells |
61%
17 Total Shells |
89%
25 Total Shells |
100%
28 Total Shells |
Buckland AF6 Combat Shotgun | 33%
23 Total Shells |
65%
45 Total Shells |
99%
68 Total Shells |
100%
69 Total Shells |
Mastaba R66 Revolver | 35%
18 Total Bullets |
71%
37 Total Bullets |
100%
52 Total Bullets |
- |
Köning PR 11 Sniper | 31%
4 Total Bullets |
62%
8 Total Bullets |
92%
12 Total Bullets |
100%
13 Total Bullets |
Techman Klust 6 Burst Cannon | 28%
18 Total Bullets |
54%
35 Total Bullets |
82%
53 Total Bullets |
100%
65 Total Bullets |
Buckland XDIST2 Choke Mod Shotgun | 33%
9 Total Shells |
67%
18 Total Shells |
100%
27 Total Shells |
- |
Techman Veruta XII Machine Gun | 31%
78 Total Bullets |
62%
156 Total Bullets |
94%
235 Total Bullets |
100%
250 Total Bullets |
Omneco EXP1 HEL Gun | 30%
13 Total Bullets |
61%
27 Total Bullets |
93%
41 Total Bullets |
100%
44 Total Bullets |
Omneco LRG HEL Rifle | 32%
9 Total Bullets |
61%
18 Total Bullets |
93%
27 Total Bullets |
100%
28 Total Bullets |
Techman Arbalist V Machine Gun | 30%
51 Total Bullets |
60%
102 Total Bullets |
91%
153 Total Bullets |
100%
169 Total Bullets |
Malatack HXC Heavy Assault Rifle | 32%
47 Total Bullets |
62%
93 Total Bullets |
94%
140 Total Bullets |
100%
149 Total Bullets |
Drekker INEX Drei Scattergun | 36%
5 Total Shells |
71%
10 Total Shells |
100%
14 Total Shells |
- |
Shelling Arid 5 High Caliber Pistol | 33%
12 Total Bullets |
67%
24 Total Bullets |
100%
36 Total Bullets |
- |
Drekker Del P1 Precision Rifle | 33%
16 Total Bullets |
67%
33 Total Bullets |
100%
49 Total Bullets |
- |
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