"The Mk110 guns would have been integrated into the Zumwalt's advanced combat system. The 30mm Bushmaster, on the other hand, is a standalone and self contained system that is as close to 'plug and play' as you can get for the capability it provides. The operator literally sits inside the cupola and directs the cannon using thermal and electro-optical sensors built into the turret".Consider the source before jumping to any conclusions.
The US planned on putting 57mm guns on their Zumwalt destroyers but used 30mm guns instead to save weight and reduce cost. These are secondary armament to provide close in defence against small boats and 30mm is considered adequate for that (although you'd never know it if you had been following the OPV thread where someone was insisting that the 30mm gun was useless and only a 76mm gun would do for this). I'm not sure what the weight issue is with the ships, but it was apparently a factor in this decision as well.
The Zumwalts are considered to be a massive failure and the US was looking to cut their losses on them. The 57mm would have required integration into the ships' fire control system, while the 30mm gun is self contained and could be just bolted on cheaply. They have deleted a number of other advanced features from the ships just to get them into service without sinking more money into them than they had to. The radar has also been downgraded, stealth more or less binned or at least not a consideration any more, and the special ammunition for the main guns (155mm) has been cancelled, rendering the main feature of the ship pointless. Cutting the 57mm guns is just one small part of a lot of corners being cut on those ships.
The Navy has replaced two 57mm guns planned on the Zumwalt-class guided missile destroyer designed to fight off swarm boat attacks with a smaller pair of 30mm guns, Naval Sea Systems Command (NAVSEA) told USNI News on Monday. The trio of Zumwalt-class ships were originally designed to field the...news.usni.orgThe 30mm Bushmasters don't come without controversy. The ship was originally slated to get much more capable 57mm guns housed in stealthy enclosures.www.thedrive.com
Meanwhile BAE sold more 57mm guns to the US for installation on other ships a few months ago.
BAE has won a $22.7 million contract to supply the US Navy with Mk110 57mm guns.ukdefencejournal.org.uk
The Germans have just bought some as well.
"Installing the MK46 Bushmaster 30mm gun system aboard a San Antonio class amphib".
The 30mm Bushmasters don't come without controversy. The ship was originally slated to get much more capable 57mm guns housed in stealthy enclosures.