Wonder if we see a M778? Basically an improved M777, built for more sustained fire.
Hard to do. The need for these guns is to support light airmobile, airborne forces but the big issue is that range is dependent on weapon mass. You can product improve the gun through modifications but a whole new gun would probably have the same issues. Remember that this gun basically replaced the M198 which weighed 15,700 lbs with an L39 barrel compared to the M777 at 9,300 lbs with an L39 barrel. That's 6,000 lbs less mass. You need a certain amount of that mass to make a stable and robust platform. I think the M777 is as light as you can go with foreseeable technology.
IMHO the M777 will fall out of use in SBCTs and maybe even IBCTs in favour of wheeled SP guns which can take a longer barrel and autoloader hence more range and bigger terminal effects. Sustained fire is an interesting concept. Most of the SPs, especially the ones with autoloaders, carry limited on-board ammo (give or take 30-40 rounds) That means they need to bomb up regularly or have a very good limber vehicle (like the M992) which can stay with the gun and replenish on the go. The other meaning behind sustained is robustness. Longer ranges means more wear on the barrel and other components - its basic physics. Personally I think that such guns should be built with quick change components to be carried out pretty far forward. It shouldn't take the manufacturer to change out a barrel. That said, these things are getting more complex every day which makes them more susceptible to breakdown. I sure as hell hope that people are taking good stock of what's going on in Ukraine. I think that there are a lot of good lessons about weapon design and sustainability coming out that need to be dealt with. Especially by Canada.
There were originally a thousand M777s in the US inventory which is more than enough to meet the needs of the airborne/airmobile forces equipped for a long time as ones in the SBCTs are replaced (and perhaps even in Active Army non airborne/airmobile IBCTs) I also think there is a good use still in the M119s. If you can't make a better lightweight 155mm and you've got a good supply then there is no incentive to build an M778 (or M1377 or whatever number comes next.)
Remember too that the Yanks still make their own barrels and about 70% of the components for the M777s so they are not about to go the road of the C3.
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