Comparison of 50mm Bushmaster III with the 30mm Bushmaster II. By comparison the 25mm’s length over all is 105.2 in (2.672 m) and its barrel length is 85.6 in (2.175 m)
SNAFU has a discussion about what up-gunning Infantry Fighting Vehicles might mean to land warfare and included the graphical information above.
The dimensions provided give us some clues about the characteristics of the gun that were not available before. Length of the barrel in calibers (bore diameter) tells us something about the gun. You usually see it written as caliber/length in calibers, e.g. 5″/38 where 5″ is bore diameter and the barrel is 38 time 5″ in length. Length in calibers suggests other characteristics including muzzle velocity, time of flight, flatness of trajectory, accuracy, and penetration ability relative to other weapons of the same caliber. Greater length in calibers usually translates into higher muzzle velocity which imparts a flatter trajectory to a given range, which usually translates into greater accuracy and better penetration ability relative to other weapons of the same caliber. Larger caliber weapons might, and usually do, exceed these characteristics even using relatively shorter length calibers.
The Coast Guard uses or has used 5″/38s, 3″/50s, 76mm/62s, 57mm/70s, and 25mm/87s. In each case, greater length in calibers translated to higher muzzle velocities.
The barrel length for the 50mm indicated in the diagram above, 117.6″, translates to a length of 60 calibers, so we should expect a muzzle velocity similar to that of the 76mm/62 Mk75 (3,000 – 3,024 fps (914 – 925 mps)), perhaps slightly lower.
There are not a lot of contemporary weapons of similar characteristics. Perhaps the closest was a Soviet 45mm/78 anti-aircraft gun with a maximum ballistic range (firing at an elevation of 45 degrees) of 12,140 yards (11,100 m). Certainly the 50mm’s performance will exceed that of the Soviet 43mm/46 which had a max ballistic range of 10,060 yards (9,200 m).
On a more practical basis this probably means that, while the Army claims an effective range of 4000 meters (probably against another Infantry Fighting Vehicle), even without guided projectiles, it would start scoring hits against larger maritime targets at 7,000 yards, which was the maximum range we used to train 3″/50 crews for, using local control. In any case it would be able to engage from beyond 4000 yards which I believe would be the maximum effective range of any improvised armament available for use on even a terrorist vessel.
Looking at the two rounds mentioned above, Programable Air Burst Munition-tracer (PABM-T) and Armor Piercing Fin Stabilized Discarding Sabot-tracer (APFSDS-T).
- The APFSDS-T is probably going to have a better chance of disabling a large marine diesel engine than any weapon we currently have in service.
- The PABM-T should be effective against personnel in small fast highly maneuverable vessels and the programable feature means misses will detonate before going any great distance beyond the target, minimizing the possibility of collateral damage. It might also be effective against drones.
Thanks to Lee for pointing me to this information.