Velocity of the Longhorn pistol is only 577.5 m/s, or 0.75x the initSpeed of .308 ammo. This is way too slow compared to real figures and the weapon has low damage as a result.
Unlike, for example, the sawed-off Mosin (which has only a 10-inch barrel), the Longhorn barrel is not particularly short. Since it is a break-action single shot, it can pack a longer barrel into a shorter length because it does not require a bolt and feeding mechanisms, etc, behind the barrel. Many modern 7.62x51/.308 rifles, such as the SCAR-H, HK 417 or L129A1 have 16 inch barrels. The Longhorn has a 14-inch barrel (measured by picture of the 3D model in DayZ, a standard T/C Encore pistol barrel in real life is 15", the DayZ version appears slightly shorter)
The standard .308 CIP test barrel has a length of 23.6 inches, the same as the Blaze rifle in DayZ. The standard SAAMI test barrel is 24 inches.
So we can compare to the Blaze the velocity of the Longhorn, and then compare to real life:
Muzzle velocity as proportion of standard 23.6" barrel velocity
Longhorn (14" barrel) = 0.714x
Blaze (23.6" barrel) = 1.00x
And now compare to some real and simulated figures for .308 fired from 14-inch and 24-inch barrels:
Bill Marr from RifleShooter.com found that a 24-inch barrel produced a velocity of 2909 ft/s with Winchester 147 gr FMJ .308 ammo. From a 14" barrel the figure was 2559 ft/s with the same ammunition, which is 88% as fast.
Muzzle velocity as proportion of standard 24" barrel velocity
RifleShooter.com test 14" barrel: 0.88x
RifleShooter.com test 24" barrel: 1.00x
To add a second source, the following load was entered into internal ballistics software "Gordon's Reloading Tool" (version 2021.1980.NIGHTLY):
Barrel length: 23.6 inches
Cartridge: .308 Winchester
Bullet: General Dynamics 147 gr FMJBT
Case capacity: 56 grains H2O
Cartridge length: 2.800"
Powder: 48 grains Hodgdon BL-C(2)
The predicted velocity was 2864.0 ft/s. Changing the barrel length to 14 inches resulted in a velocity of 2503.4 ft/s for the same load, which is 87% as fast.
Muzzle velocity as proportion of standard 23.6" barrel velocity
GRT 14" barrel: 0.87x
GRT 23.6" barrel: 1.000x
It is worth noting the kinetic energy is reduced by the square of the decrease in velocity, so a weapon that has 88% of the standard 23.6" barrel velocity will only have 77% of the kinetic energy.
But either 88% or 77% are both significantly more than the current ~71% velocity/damage as compared to the Blaze!