The 25mm guns (M242) in the Mk38 mounts that are the main armament on the Coast Guard’s 210 foot, Webber class, and Island class Cutters are part of a family of electrically powered guns marketed by Northrop Grumman, referred to collectively a “Bushmasters.” The 25mm is also used on the Bradley fighting vehicle and the Marine’s LAV 25 wheeled fighting vehicles. A slightly larger version, the Mk44 30mm is used on the San Antonio class LPDs, Littoral Combat Ships, and the DDG-1000 class.
Lately, the Army and Marines have become concerned that these guns are being out-ranged by adversary weapons. (I share this concern with the regard to a possible maritime terrorist attack.) This has lead to development of larger weapons of 40mm and most recently 50mm. The 50mm is claimed to have twice the effective range of the 25mm. These weapons were recently demonstrated at the “Bushmaster Users Conference,” 9-10 April, in Kingsman, AZ with a live fire demonstration at Big Sandy Range (video above). The Coast Guard may use one of these weapons in the future in place of the current 25mm.
Going from 25 to 30, 40 or 50mm may not sound like a big jump, but projectiles are three dimensional and the difference in weight and hitting power is striking.
Below are listed the maximum projectile weight in pounds associated with each caliber. I did not have this information for the 40 and 50mm chain guns, so I have used the weight of modern Bofors 40mm projectiles and an estimate based on a scaled up 30mm round for the 50mm to provide approximate values:
As can be seen, the 40mm round is about five times as large as the 25mm and the 50mm is about ten times as large.
The larger caliber is not only more destructive, it also means it is easier to include smart fuses and possibly even guidance systems.