Overheating is mostly barrel because there is obvious direct heat transfer from the burning propellant. Again obviously, the amount of the heat depends on the amount of propellant. The implication is that firing lower charge there is less heating therefore other limits permitting you can increase the RoF if necessary. I too would be amazed if 8 rds in 2 mins from a cold gun got anywhere near heat limits, an already fairly hot gun and top charge might be a different matter. As previously pointed out most armies ignore the differing heat values of different charges in their 'official' rates. And most armies tend to ignore the official rates when firing FFE, 'as fast as you can' is the long established norm and they get away with this because it's usually not the top charge. Barrel heating is a problem, and not just at sustained fire. Procedurally speaking FFE fire missions in quick succession are not sustained fire, but it doesn't make the issue disappear, a hot gun is still hot whether it fires 110 rds in 50 mins at one target or 54 rds in 11 mins at 3 tgts which is why barrel cooling attracts interest, including by 777 original designers who are reported to have tested a sub-system squirting water up the barrel for AS90 PIP. However, another problem is the recoil system this too heats up with work, of course it depends to an extent on the materials employed, and the failure is unlikely to be catastrophic but historically over worked recoil systems have probably caused more down time than overheated barrels. As previously posted I'd guess that 777's search for lightness may have reduced it's ability to absorb heat so it heats up faster than more conventional 155mm. But without comparing barrel weights and an expert thermodynamist to model the recoil it's a guess. It's a strange requirement that takes laying off the timeline for firing more than one round. The implication is that there is no laying between rounds. Some armies do allow this in some conditions, but hitherto it's always increased the spread of the fall of shot (I'm seriously impressed if 777's mounting has totally eliminated this). Given that 777 seems to have to be loaded within some elevation limits and therefore has to be relayed after loading if outside these then I'm a tad puzzled. One implication would seem to be that 777 can't even achieve 4 rpm in 'real' (ie with relaying) conditions. It's most unclear why 777 should be limited to 8 rds in 2 mins, if it's barrel and or recoil heating then it's a hell of a price to pay for light weight. If it's crew limits then either the crews are grossly idle or they are having to work a system that is ergonically bad. Manual ramming is slower than power ramming and 2 man laying is slower than single man laying, so perhaps these two factors are enough to reduce the rate to something just above the 155mm rate of WW2 when 155mm had to be loaded within narrow elevation limits. Or perhaps I'm just being unfair and this is the rate with the minimum crew not the 'normal' size crew, and the big item in the timeline is one person moving ammo several metres to the loading tray. The baseline for towed 155mm, established some 30 years ago is 3 rds in 15 sec and 6 rpm for 3 mins, naturally this includes relaying before every round after the first, (and I think FH77A can do better than this, but light it is not). The question is 'why can't 777 match the baseline'. One answer might be that the whole matter is a test construct, like is not being compared with like because 777 performance measured is under some extreme conditions that no one else has considered representative. It's interesting that 777's designers also did AS90, of course this is SP and has an semi-auto loading system, but apart from that it's fairly 'no frills' and gives 3 rds in 9 secs and 6 rpm. Its other obvious differences with 777 are a power rammer, sliding block breech, auto-laying. Perhaps there's a message here - light weight has a price.

This may be redundant as far as most of the spat thats appearing re the 777 but here goes anyway: when the 777 was still at the XM-777 stage I was involved on another project looking at the effect of recoil and ballistics impact. The XM-777 was shown as an example of how the intervention of form could impact upon function. the absolute mass of the XM-777 was seen as the main contributor to some of the problems it had with recoil, these being: -shattered optics -catastrophic fatigue on the spades - to the extent that spades were fracturing after sustained fire - barrel fatigue was considerable at ssustained fire. I'm not sure whether that was a legacy of sleeve mismatch, liner mismatch or whatever - but I do recall that in the case examples we saw that barrel life was shorter than on it's intended replacement. the whole issue of saving weight to make sure that it was air transportable was one of the factors blamed for accelerated recoil probs and fatigue problems. that was about 4 years ago, so I'm not sure whether any of that has relevance to the current fracas between some of you. btw I am not an arty - so I have no idea whether I am stuffing this up in translation from memory ;) My involvement was purely at a recoil investigation and management level for another weapons project.

ArtyTster, You are absolutely right. Not sure what neutralizer was going on about, I think he wants to impress us with knowledge even if it has nothing to do with the subject. The sustained rate-of-fire requirement for howitzer is typically that the howitzer must be able to maintain there sustained rate-of-fire requirement (in the M777 case, this is 2 rounds per minute) until the ammunition runs out or the tube overheats. There is a thermal warning device to monitor cannon tube temperature. As far as gf0012 input, the M777 has a very reliable recoil system. It did have a spade cracking issue years back, but this issue is for the most part resolved. If there are any issues with the spades they would only be in Arctic tundra like environments and in this case the are most likely mitigating procedures for these circumstances.

[ As far as gf0012 input, the M777 has a very reliable recoil system. ] I didn't say it was unreliable, I was indicating that there were legacy problems linked to recoil management. Hence the spades were increased in size, and the basic shape was reconfigured. Optic fragility was part attributed to a mounting process as well as internal construction issues IIRC. But, as I said, it's been a while since I saw the original version and change control documents.

Guns undergo development to find and fix the problems, far better to find them then than when they're in service. I actually think 777 has a lot of potential, but am firmly unconvinced that if what is on this list is anywhere close to accurate then this potential is far from being realised. It all reminds me of a fairly well known quote from a senior UK arty offr in about 1941, to the effect that 'in peacetime everyone wants mobility, in war they want firepower', seems to sum up 777 rather well. I reckon this excessive concern with kg is a w...k, a strong dose of pragmatism is needed to make sensible trade-offs between mobility & firepower. (both of which have reliability elements, with crew size, ammo packaging, push or pull logistics, etc, etc all being factors) As to rate of fire, I'll repeat my original remark, two factors - technical contraints and what the crew can achieve. I think we have agreement on this. The issue seems to be which is which with 777. Part of the problem is defining the problem in and definition of 'representative conditions', 'battlefield day' or what ever terms you use. And whatever is chosen it's always easy to nitpick it to death. Simplistic notions of bureacratic terms like 'sustained fire' are far removed from what reality can be like. Part of the problem is that the number of guns is going down in many armies and battlefield density is decreasing, this means that if you expect to make any use of traditional 'dumb' shells then guns are going to have to fire more each. Of course this really only applies in serious warfighting, when expenditure averages several hundred rounds per gun per day. If you expect dumb shells to be the exception and not having to indulge in serious warfighting then a lesser firing capability will doubtless suffice.

For rifles, some people try to go ultralight with graphite barrels, which have steel cores. Graphite handles heat better, and is way lighter. Now, mostly I see these on .22 LR, and with that caliber, the steel probably doesn't matter at all, but they make it in .50 BMG, also. I don't know if it would be practical, but it seems like such weight reductions might really help artillery.

there is a limit to how "light" you can go with an arty barrel. the issues are predominately metallurgical - and it's one of the problems (as an eg that the Russians had when designing their main guns as opposed to NATO style main guns) Someone in here could go into the philosophy of why the russians chose 125mm as opposed to NATO 105mm and eventually 120mm. It's not just the issue of a lighter barrel, there is also the issue of the liner, sleeve, then the weapons characteristics such as rate of fire, and even the causal effect of specific round types. at a certain point, and it varies with each "piece", barrels have to be changed over as they are fatigued - and in a real sense they start to stretch (in a fashion). Part of the problem with the XM-777 was it's absolute lightness requirement over it's realistic functionality requirement. BUT - big caveat here, I am talking from memory and with a vague association with a ballistics project I worked on about 6-7 years ago. So my recall may be a bit off. arty-engineer might be the best to get absolute info on this.

I forgot to add, that when barrels are cycled out for a changeover, it's not just because they fatigue and "stretch", depending on the metallurgical properties of the bore liner, sleeve, temperature variances etc of those metals, some metal will actually become "brittle". lightening a barrel will have some trade offs, and unless someone has made a dramatic breakthrough in the last few years, I don't recall seeing anything that indicates a sea change in the metallurgy issues governing heat, brittleness, fatigue etc in arty/main gun development.

Of course until after WW1 some nations, notably UK used 'wire wrapped' barrels extensively (most if not all barrels from 18-pdr upwards), ie an 'A' tube tightly wrapped with wire. IIRC this remained the UK practice with large calibre naval and coast guns until the end of WW2. It seems likely that next generation barrels will use 'A' tubes wrapped with modern lightweight materials.

so I am taking this to its logical conclusion. How much could the weight of a tube be reduced if it fired only one shot? It could be made of composites which fail or even self-destruct after firing.