“Weapons Effectiveness Testing–25 vs 30mm” Revisited

I am resurfacing this old post from 2017, because our weapons effectiveness is still an issue. I also reformatted a couple of sentences to bold type face, so the points would be harder to miss. Hopefully the Mk38 Mod4 will have at least the 30mm gun, if they don’t decide to recycle 25mm guns, as seemed to have been the case when the Mod3 changes were minimized compared to the Mod2. We really need to upgrade the older mounts to a more effective weapon, otherwise we are planning to fail. Either replace the 25mm with a more effective gun or add APKWS or Hellfire/JAGM small missile systems. Better yet, do both.


This is old. It goes back to 1992, but if they knew the results here, it raises a question, why are we still equipping the Mk38s with 25mm guns instead of 30mm (or 35mm or 40mm) guns which also fit the same mount? The results are discussed beginning at time 8:00. The 30mm does nine times the damage to the hull and five times the damage inside the hull.

At the very least we need to make sure we have available rounds that do not detonate on impact. The 25mm rounds, exploding on impact, failed to even penetrate the 1/4 inch aluminum hull of the Mk3 target boat.

Thanks to Luke for bringing this to my attention. 

17 thoughts on ““Weapons Effectiveness Testing–25 vs 30mm” Revisited

  1. At what range though! Link doesn’t give the range at which to Mk.3 PB was engaged at! Maximum range of 25mm/87-caliber Mk.38 is ~7,450-yards and Effective Range at ~2,700-yards! It also doesn’t state what ammunition type was being used, whether APDS, APDS-T, HEI, HEI-T, SAPHEI, SAPHEI-T or FAPDS-T… And the APDS-T has an ~1,100-yard range advantage over the HEI-T…

  2. I’d prefer we get away from Mk 38 altogether. I think we need to use something already available. For simplicity, I’d use the 30mm remote turret they are going to use on the Amphibious Combat Vehicle. Plan that way with the notion of future, larger non deck penetrating mounts.

    • OK, but the Kongsberg MCT-30 Turret weighs ~7,716-pounds without the gun! What are you adding or subtracting from your Small Cutter to compensate for the additional weight…

      • Video mentions that Test Gun used to fire the 25mm Ammunition was the GAU-12 which isn’t the same as the Mk.38 uses. The Mk.38 uses an 87-caliber barrel, whereas the GAU-12 uses a 69.3-caliber barrel. Also video doesn’t mention what test gun was used to fire th3 30mm ammunition. Also keep in mind that the effective range of GAU-12 is ~1,200-yards. And trying to hit and penetrate 1/4″ of Aluminum at 3,000-meters is severely pushing what the GAU-12 can achieve in a near flat trajectory…

      • Bottom line, the 30mm is a lot more effective than the 25mm. I really think we need something with an effective range of at least 4,000 yards if we are going to avoid the possibility of having the cutters weapons taken out by improvised weapons.

        Greater range allows you to protect not only your own unit, but other units as well.

        If it is a question of taking on a swarm, then you don’t want to wait any longer than you have to before you start taking them out.

      • Probably so, but willfully testing a specific ammunition type from two different calibers (i.e. 25mm vs. 30mm) using guns not normally being employed isn’t a fair test. The GAU-12 isn’t used by the USCG or the US Navy on any surface ship. The GAU-12 is typically employed on Aircrafts and should have been test that way on an Aircraft…

      • This test was done back in 1992 when only very few Mk38 mounts were out there and I believe before there was the 30mm Mk46 mount. They were comparing the two round, and they seem to have done good job. The fact that 3000 yards is a stretch for the 25mm does not mean it gets extra points, if that is a range that is considered relevant, as apparently that was the case.

      • But how is that a Fair Comparison when the Barrel Length of the 30mm/89-caliber Mk.46 tof the GAU-12’s 25mm/69.3-caliber. Barrel length of the Mk.46 in inches is ~105.2″ in length compared to the GAU-12’s 68.2″ barrel length. The only Navy that uses the GAU-12 variant on it’s surface units is Italy and it’s barrel length is 80-caliber or ~203.2″ in length…

      • MCT-30 is a confusing label from what I’ve seen. The army’s appears to be the MCT-40 (5400lb) and the Marines MCT-20 (2700lb). No reason to weigh the turret down with protection the rest of the ship won’t have.

      • @ Andy.

        The ammunition is stored in the turret of the MCT-30, the reason it was chosen to still allow the vehicle to be able to carry it’s 8-man detachment…

  3. The neither of the guns used to fire the rounds in the test were the same as the guns currently used on naval vessels, but they were very close to what followed and are representative of the results using the ammunition they had available at the time.

    The test weapons were
    25mm GAU-12 HEI muzzle velocity 3,560 feet/sec
    30mm GAU-8 HEI muzzle velocity 3,324 feet/

    Our current systems are
    25mm Mk242 HEI muzzle velocity 3610 feet/sec
    30mm Mk44 HEI muzzle velocity 3543 feet/sec

    In both cases, the current systems perform better than the test article. The improvement is much greater in the case of the 30mm.

    The other change of significance is that there is now a 25mm APDS (armor piercing discarding sabot) round that would almost certainly have been able to penetrate the 1/4″ aluminum hull of the 65 foot patrol boat but that projectile includes no explosive so damage would have been localized.

    • Also keep in mind that both guns were fired on “Dry Land” where the Land Surface “doesn’t” move, and test vessel were in nearly calm waters. Test should have been done on a Test Ship against Test Targets in something actually resembling conditions that the Real Vessel at Sea is likely to encounter…

      • Not really. It was only a test of the effects of the projectiles fired at representative ranges against representative targets. There are certainly other issues of importance but they would only become important when the gun mounts are developed. At that point it was a question of the choice of round between two likely candidates.

      • As you said previously that both test guns were NOT the type of guns that would normally be used and in a previous comment quoted that the 30mm was more destructive than the 25mm fired at the same ranges. 3,000-meters is pushing the envelope in performance for the GAU-12 fire on dry land and at a near flat trajectory to the horizontal plane, something the GAU-12 wasn’t meant to do, being the fact that aircrafts in flight rarely if ever fire in a near flat trajectory to the horizontal plane, unlike those of Naval Guns which do fire near flat trajectories to the horizontal plane…

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