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.
Chuck Hill's CG Blog 
Chuck, I am relatively sure the 40mm they are talking about is not the 40mm Bofors. It is the 40x180mm Super 40. It is based on the 30x173mm cartridge. Fired from a modified Mk44 Bushmaster II. This is in the same manner as the 50mm is more or less a descendant of the 50 Supreshot developed from the 35x228mm cartridge. Fired from an adapted Bushmaster III cannon.
My understanding is that the Army has never been a fan of the 40x365mm due to the space needed for it’s ammo feed and storage system.
Click to access WednesdayReunionRickWright9945.pdf
Click to access CANNON2.pdf
@FDD, thanks for the link. The difference in penetration is nice to see.
I know it is a different round, and I thought I made that clear in the post, but the weight of the projectile is probably very close. As noted, I only used the Bofors projectile weight because I could not find a weight for the 40×180 projectile. There is a picture of the 40×180 “40mm Super Forty” alongside the 30mm round in the NavWeaps entry on the Mk44 gun.
http://navweaps.com/Weapons/WNUS_30mm_BushmasterII.php
One of the remarkable things is that the Army expects to stow as many 40mm rounds as they currently do 30mm.
I’ve always been a fan of the Super 40. Seems to check a bunch of boxes for the Army.
The gun and rounds occupy the same volume as the 30mm, while having near 35mm penetration. The 40mm HE round has a significantly bigger bang than the 30mm.
The 50mm EAPS/Super seems like both a bit too much and way too little gun for an IFV.
It’s a bit too much because 30/40mm is probably sufficient to penetrate the vast majority of IFVs we can be expected to face at useful combat ranges. So 50mm is overkill vs IFVs and other light armor. That overkill comes at a cost of fewer “stowed kills”, meaning fewer 50mm rounds can be carried than Super 40.
What’s unclear to me is whether a combat load of 50mm is more or less effective (due again to “stowed kills”) vs other types of targets (e.g. buildings, infantry in defilade or in the open). A single 50mm round is likely more effective against these targets than a single Super 40mm round, but if I can carry two or more Super 40 rounds for every 50mm round, maybe the balance goes in the other direction.
It’s too little gun because it can’t engage tanks any better than Super 40 or 30mm or even 25mm.
So it’s in this weird ‘tweener area.
Now if the 50mm guided projectile works out, one thing it might do significantly better is engage UAVs and potentially RAM targets (Rocket, Artillery and Missile). But it will need a significant fire control and sensor upgrade to make use of this.
Given Russian tactics in Crimea, this could be a major advantage.
The Army is currently looking to replace the Bradley. Their RFP reportedly includes a 30mm as threshold requirement and a 50mm as objective. They not only want to kill hostile IFVs, they want to do it at greater range.
The rationale they use for their decision doesn’t effect us, but the final choice of a weapon probably will determine what is a practical choice for the Navy and in turn for the Coast Guard. If the Army chooses a 50mm, I think we will see the availability of a 50mm naval mount as well, if not then I would expect a 40mm.
It would be interesting to see how they derived that threshold and objective requirement. Seems to me it isn’t well-formed. The requirement should be more like “defeat projected IFV threat at 2,000m (threshold), 3,000m (objective)”. Which then begs the question, is the projected threat a BMP-3M? Kurganets-25? T-15 Armata?
Based on what little I’ve read, the first two can probably be penetrated by 30mm or 40×180 at anything short of extreme desert ranges.
The T-15 likely can’t be penetrated frontally by any of these cannons at any range, short of a lucky shot.
Agreed that the Army’s rationale vs Navy/USCG/USMC’s rationales are different.
Chuck it right this post.
The 50mm gun SHOULD become the secondary gun of choice, i.e. principle defensive weapon on most USN warships. And main gun for most smaller combatants (when the Navy gets around to replacing the Cyclones).
Its about time the USN move beyond 25mm and 30mm guns for secondary weapons on its blue water warships~
I don’t know if there is currently a naval mount appropriate for the 50mm. Hopefully we will see one soon, but if the vender is to be believed all the current 25 and 30mm guns could be converted to 40mm by changing the barrels and a few parts.
Of course they probably would not bother to do that if they were planning on wholesale replacement with 50mm. First to get them would probably be LCS and LPDs.
Since what we have seen on the “Polar Security Cutter” so far looks like two Mk38 remote weapon stations, would sure like to see those turn out to be 50mm.
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While the 50mm carries more punch, the worldwide availability of 40mm rounds has to be considered. It’s going to be awfully expensive to be the only major player with a 50mm need.
If the Army adopts this–and that is the only way this could work–they will be produced in quantity.