Physical bounds

Limits no gun can break: how far a projectile can fly with no air, how fast a gun is pushed back by its bullet, and the order things happen in.

Range with no air

Air only slows a projectile, so the furthest anything fired at a given speed can land on level ground is the range it would reach in a vacuum, launched at 45 degrees. A recorded maximum range beyond it is impossible, whatever the gun, unless the projectile keeps pushing after it leaves the muzzle: rockets are exempt.

R_{\max} \leq \frac{v^{2}}{g}, g = 9.80665 m / s^{2}

where

$R_{\max}$: the recorded maximum range, in m
$v$: the recorded muzzle velocity, in m/s
$g$: standard gravity

The Milkor MGL, from its record: 76 m/s at the muzzle and a maximum range of 800 m.

$\frac{76^{2}}{9.80665} = 589 m$

The furthest it could fly with no air

0 m589 mrecorded: 800 m

Answer: 800 m is beyond the 589 m bound, so the range or the velocity belongs to another load.

Recoil from momentum

A bullet leaving the muzzle carries momentum, and the gun takes the same momentum backwards: the gun's recoil velocity is at least the bullet's mass times its velocity over the gun's mass. The powder gas adds to it, so this is a lower bound, and it needs no figure the record does not already hold.

v_{r} = \frac{m_{b} v}{M} \leq 15 m / s

where

$v_{r}$: the speed the gun is pushed back at, in m/s
$m_{b}, v$: the cartridge's typical bullet mass, in kg, and the muzzle velocity, in m/s
$M$: the gun's empty weight, in kg

Across the catalogue the median gun recoils at 2.2 m/s from its bullet alone and the 99th percentile at 7.2. The most violent real guns in it, a .45-70 derringer and a pocket percussion derringer, reach 13 to 14 m/s, so the line is 15 m/s: beyond it the gun's weight is usually a part's (a receiver, an upper), or the gun is linked to the wrong cartridge. Launched rounds (grenades, flares, darts, pellets) are exempt.

The Radian AX556, from its record: 230 g, firing a 4 g bullet at 914 m/s.

$v_{r} = \frac{0.004 \times 914}{0.23} = 15.9 m / s$

Recoil from the bullet alone should stay under

0.0 m/s15.0 m/srecorded: 15.9 m/s

Answer: 15.9 m/s is past the 15 m/s line, so the weight is probably a part's rather than the rifle's.

Order and containment

A variant is not introduced two or more years before the gun it is filed under: one year is wrong, or the variant is filed under the wrong gun (the M40A1 of 1977 was filed under the M40A5 of 2009).
A sight radius is not longer than the gun its sights sit on.
An effective range is not longer than the maximum range.

How a record is judged

Table 3. How a record is judged against the physical bounds. Rows are read in order; the first that applies decides.
#	When	Verdict	What it means
1	A rocket projectile	Set aside	Set aside from the range bound: it keeps accelerating after it leaves the muzzle.
2	$R_{\max} > \frac{v^{2}}{g}$	Impossible	Further than the projectile could fly with no air: the range or the velocity belongs to another load, or is in feet or yards.
3	$R_{eff} > R_{\max}$	Impossible	An effective range beyond the maximum range: one of the two is wrong.
4	A launched round (grenade, flare, dart, pellet)	Set aside	Set aside from the recoil bound: it is thrown, not fired.
5	$\frac{m_{b} v}{M} > 15 m / s$	Review	Pushed back faster than any gun a person holds: the weight is a part's, or the gun is linked to the wrong cartridge.
6	$L_{sight} > L$	Impossible	Sights further apart than the gun is long: the radius or the length belongs to another variant.
7	$Y_{variant} \leq Y_{parent} - 2$	Review	A variant two or more years older than the gun it is filed under: a year is wrong, or the variant is filed under the wrong gun.
8	Anything else	Holds	Within every bound.

Range with no air

Recoil from momentum

Order and containment

How a record is judged

Checks that use this method