"Eventually, I realized that at least part of what was happening was that the gunpowder filling was moving inside the shell cavity when the round was fired, and the friction heat that generated was causing the premature detonations. So I tried stabilizing the charges by pouring in hot tar to hold everything in place. I had to be careful to preserve an open channel for the fuse's flash to reach the main charge, but that wasn't too difficult.
"After I started using the tar, we got no more premature detonations. . . as long as we stuck with the solid plugs, instead of using live fuses. That seemed like pretty conclusive evidence that the shell wall was strong enough, but I wanted to be sure. So, I filled several dozen shells with flour, instead of gunpowder, put live fuses into them, and fired them into shallow water where divers could recover them. When I examined them, it was obvious that the fuse itself—or enough of it to do the job, at any rate—was being blown into the shell, but that the walls weren't cracking under the stress of firing, which confirmed my suspicions about the cause."
He paused for a moment, his expression that of a man torn between satisfaction that at least a part of his design had proved workable and that he'd devised a technique for proving that it had, on the one hand, and frustration over his inability to fix the part of the design that hadn't proved workable, on the other hand.
"It doesn't happen every time, of course," he said then. "But it does happen a lot of the time, and getting gunners to adopt something this newfangled is going to be hard enough even if they're not afraid each shell is going to explode either inside the gun or the instant it clears the muzzle. It's just a little difficult for them to feel all warm and happy about something that's likely to kill them, you know."
"Well, yes, I can see that, I suppose." Merlin smiled slightly. Then he tugged on his mustache again, his smile turning into a frown as he pondered.
"Tell me," he said finally, "from what you've just said, it sounds as if you were loading the guns with the fuse hard up against the propelling charge."
Seamount nodded, and Merlin raised one eyebrow.
"Have you considered loading your 'shell' with the fuse facing away from the propelling charge, instead?"
"What?" Seamount frowned.
"I asked, if you'd—"
"Just a minute!" Seamount's raised hand stopped him, and the stubby commodore's eyes narrowed as he thought hard and furiously, indeed. Then he started nodding. Slowly at first, then faster and faster.
"Of course! I should have thought of that myself! The flash from the propelling charge sweeps all the way around the shell, doesn't it?"
"I'd certainly think so, at any rate," Merlin agreed.
"Of course it does! And if it sweeps around and lights the fuse in the front instead of hammering it into the shell cavity from the back. . . ."
Seamount stepped over to one of the slate-covered walls, snatched up a piece of chalk, and began jotting notes to himself. He read over them, shook his head impatiently, erased one line and chalked a correction, then nodded and looked back over his shoulder at Merlin.
"You're a very useful fellow to have over on a visit, Seijin Merlin," he said dryly. "Somehow, you always manage to point me in the right direction, don't you?"
"One tries," Merlin murmured.
"Oh, one certainly does," Seamount agreed.
"Was there anything else I might help you with, My Lord?" Merlin asked, sounding as little as if he were changing the subject as he could manage.
"Actually, there are two other problems I wanted your opinion on."
"Of course, My Lord."
"Both of them have to do with the new rifled guns," Seamount began. "I've tried several approaches to getting their rounds to take the rifling. One that seemed promising was to encase the projectile in a soft metal, like lead, that could be forced into the rifling much as we've done with the new rifle bullets. Unfortunately, the lead keeps stripping off and the rounds don't take the rifling consistently.
"One of my bright young assistants suggested that what we might do was to cut the cannon's bore like a helix, so that it was twisted itself. Not a round bore, you understand, but something a bit more trapezoidal that twisted around its own central axis to force the shot to spin without requiring rifling at all. Frankly, I think that would probably work, but I'm concerned about bore erosion. Which is why I'm still convinced that some form of grooved rifling is the answer; it's just a question of figuring out how to make the shot physically engage with the grooves.
"So far, the most promising thing I've tried is to cast the shot with metal studs." Chalk cracked like a staccato explosion as he tapped one of the diagrams on his wall. "As you can see, the idea is that when the gunners insert the shot into the muzzle, they engage the rifling with the studs. Then the shot rides down, rotating as it goes, until it comes to rest against the propelling charge. When it's fired, the studs ride back up the grooves, which imparts a rapid spin to the shot, and off it sails to its target."
He turned back from the wall to smile fiercely at Merlin, and Merlin smiled back.
"The problem is this," Seamount continued, his smile fading slightly. "First, as we'd expected from the beginning, bronze is too soft, especially using the stud-and-groove system. The insides of the barrels simply shred after only a very few rounds. Secondly, I've already discovered that even with the stud-and-groove approach, bore pressures are rising dangerously."
"What do you mean, 'even with the stud-and-groove approach'?"
"I expected bore pressure to go up drastically when I tried the lead coating system. After all, the shot was sealing the bore a lot more thoroughly, so it was inevitable the pressures would go up, the same way they went up in the rifles when we started using hollow-based bullets in them. But I'd rather hoped that enough of the propelling gases would be able to escape around the shot, which is smaller in diameter than the bore, using the stud system. Which, by the way," he added parenthetically, "is one reason I'm irritated with myself for not realizing those same gases could ignite the fuse on their way past the shell. Anyway, I'd hoped the windage between the shell body and the bore wall would let the gases escape and relieve the pressure."
"I can see that," Merlin acknowledged.
"Well, I suppose at least some of the gases are doing just that," Seamount told him. "Unfortunately, I don't think enough of them are. And there's another factor, too—one I hadn't really thought about initially. The shells we're developing for the existing smoothbores are the same size as the round shot they already fire, and because they're filled with gunpowder rather than solid iron, the shells are actually lighter than the shot the guns were originally proved for. But in a rifled gun, the shot doesn't have to be round. In fact, you don't want a spherical round. Since a more cylindrical shape lends itself more efficiently to rifling, anyway, you end up with an elongated projectile. For an explosive shell, that will give me a larger internal cavity, which means I'll be able to pack in more explosive, and the fact that it's hollow will tend to hold the weight down, at least to some extent. For a solid shot, though, the overall weight of the shot goes up very sharply, and even with a gunpowder filling, a properly designed shell strong enough to stand the shock of firing without disintegrating is going to have thick enough cavity walls for it to weigh more than a round shot for the same gun. And that greater weight means the gun has to work harder to throw shells at the same velocities at which it throws round shot, and that drives up bore pressure, too."
"All right," Merlin said, nodding to show he was following so far.
"We can cast iron guns and then cut the rifling grooves into them," Seamount said. "On the other hand, we've already got hundreds—thousands, actually—of the new bronze guns. I'm sure we could find something else to do with all of that bronze, but it seems an awful pity after we've gone to all the trouble of casting them in the first place to simply throw them away—as artillery pieces, I mean. That's one problem. The other problem, frankly, is that cast iron is a lot more brittle than
bronze. I'm not sure it's going to be up to the stresses that are going to be exerted once we start casting large-caliber rifled guns. Not without going to truly enormous pieces—probably at least as big as or bigger than the old Great Doomwhale."
Which, Merlin reflected, had weighed almost six tons.
"But what would you use instead?" he asked aloud.
"At the moment, I'm thinking in terms of wrought iron," Seamount replied, not to Merlin's great surprise. "It'll be expensive—even more expensive than bronze—but Master Howsmyn says his ironmasters are equal to the task. I think he's probably right about that, but producing reliable wrought-iron gun tubes is going to be expensive in terms of manufacturing time, as well."
Merlin nodded again. He wasn't surprised by the difficulties Seamount had encountered. Indeed, if he was surprised at all, it was by how quickly the Charisian had experienced them. Which was foolish of him, he supposed. If Sir Ahlfryd Hyndryk had demonstrated anything, it was that his mind was every bit as quick and focused as Prince Nahrmahn's, if in very different directions.
The problem, as Seamount had just pointed out, was that cast iron was brittle. Safeholdian foundry techniques were remarkably advanced for a culture where steam power had been prohibited, yet they still weren't up to mass production of steel by a considerable distance. The technology itself lay within their grasp, but there were still obstacles to be overcome.
The fact that Safeholdian foundries had been using waterwheels for centuries helped, but it was only in the last few decades that men like Edwyrd Howsmyn and his "mechanics" had begun applying power to the process more generally. Initially, the waterwheels' only true function had been to power blowers to raise the temperature in Safeholdian blast furnaces and fineries. The processes for turning blast furnace iron into wrought iron and steel had been no further advanced than perhaps 1700 Europe.
Howsmyn had been one of the pioneers—all of whom had been located right here in Charis—who had championed replacing charcoal with coke made from the kingdom's generous quantities of coal. He'd also taken the lead in developing what had been called the "puddling process" back on Old Earth, with the result that his foundries' output of wrought iron—very high quality wrought iron, in fact—was several times that of any other foundries on Safehold. But even though that was true, wrought iron was still more expensive, primarily because of the greater amount of labor, processes, and time involved in its manufacture, than cast iron.
There was plenty of room for refinement in his current relatively crude techniques, but what he'd done so far hadn't truly required Church approval, since it was based entirely on novel applications of techniques which had already been approved. On the other hand, all of them were basically empirical. They'd been worked out by men with lifetimes of practical experience forging iron and steel, but with no theoretical understanding of why the improvements they'd come up with worked. Any systematic effort to tweak Howsmyn's current capacity was going to require the development of that theoretical understanding, and that was going to be a problem in the face of the Proscriptions of Jwo-jeng.
The crux of Seamount's current problem, however, was that the only alternatives for artillery pieces were bronze, cast iron, and wrought iron. Bronze was an excellent material for smoothbore muzzleloaders, but, as Seamount had just complained, it was both expensive and too soft to stand up to the strains of rifling for very long. Cast iron was relatively cheap, and the foundry techniques for working with it were well established, but even using sandcasting to reduce porosity, cast-iron guns were much more brittle than bronze and likely to crack or burst under the stresses of the bore pressures Seamount was anticipating. Which really left only wrought iron. If Ehdwyrd Howsmyn said his foundries could produce the needed guns out of wrought iron, Merlin had no doubt they could, but Seamount was right that they weren't going to be cheap.
"All right," he said finally, "I've got a couple of thoughts.
"First, as far as the existing guns and the bore pressures are concerned. If I'm understanding you correctly, you're saying that if we're willing to accept a lower shell velocity, we could probably keep pressures within the acceptable limits for the existing gun tubes, even with the heavier shell weights. Is that pretty much correct?"
Seamount nodded, and Merlin shrugged.
"In that case, why don't you ask Master Howsmyn if it would be possible to produce a relatively thin-walled, rifled tube, like an inner sleeve of wrought iron, that we could slide down inside the bore of an existing smoothbore? What I'm thinking is that if we did that, and fixed it firmly at the muzzle, probably by cutting threads into the outside of the muzzle and literally screwing its forward end into place, then fired a fairly powerful charge out of the gun, wouldn't it expand the inner sleeve and more or less weld it into place as a permanent liner that would protect the bronze against bore erosion?"
"I. . . don't know," Seamount said slowly. "It sounds like it ought to make sense. At any rate, it's certainly something to ask Howsmyn about."
Chalk rattled as he jotted additional notes. He stood back to read over them and frowned thoughtfully.
"The strength of the existing gun tubes would still limit shot weight and velocity," he said. "You're right about that. But we've got enough margin to handle heavier projectiles than the guns are firing now, I think. And the increase in accuracy, not to mention the use of an explosive filler, would make the idea more than worthwhile if we can figure out how to do it."
"That's what I thought, too," Merlin agreed. "On the other hand, I had another thought when you were talking about why wrought iron was better than cast iron."
"Ah?" Seamount turned back from the slate wall, eyebrows rising.
"Yes. You said cast iron is too brittle to stand up to the bore pressures you're expecting."
Seamount nodded, just a touch impatiently, and Merlin shrugged.
"Well, what occurred to me was that while you're right, that wrought iron is less brittle, that might not be the only way to get the strength you're looking for."
Seamount looked perplexed, and Merlin waved one hand, like a man trying to pluck the exact word he wanted out of the air.
"What I'm saying is that you're thinking in terms of a solid mass of metal strong enough to stand up to the discharge of these new rifled artillery pieces of yours."
"Of course I am. You're not suggesting we make them out of wood, are you?"
"Not quite." Merlin grinned at the asperity which had seeped into Seamount's tone. "The point that had occurred to me was that perhaps Master Howsmyn should be looking into another approach. What if instead of trying to cast the cannon as a single, massive piece of metal, then reaming out and rifling the bore, he used a relatively thin wrought-iron tube, like the 'sleeve' we were talking about a few moments ago. But instead of sticking it down inside an existing bronze gun tube and expanding it, what would happen if he wrapped it very tightly in wire, instead?"
Seamount opened his mouth, as if to automatically dismiss the idea, then froze. His eyes widened in sudden speculation.
"What you're saying is that we could wrap the reinforcement around a fairly light tube," he said slowly. "I don't see any reason that couldn't work, as long as we wrapped it tightly and thickly enough."
"I'd think a wire-wrapped approach would be a lot less brittle than cast iron or even wrought iron," Merlin agreed. "Surely the individual wires would have a tendency to flex and stretch without cracking or bursting the way solid metal might under the same pressures."
"Not only that," Seamount said with gathering enthusiasm, "but you wouldn't have to wonder if there were flaws, the way you do with iron. You'd be able to examine every inch of wire individually before it went into the gun!"
"Yes, you would." Merlin's approving surprise wasn't at all feigned. Once again, Seamount's agile brain was leaping ahead as soon as the possibilities were pointed out to him.
"I don't know if it's practical, at least with Master Howsmyn's existing equipment," the
Charisian said, almost bouncing up and down on his toes as his mind careened through the vista of possibilities and the accompanying manufacturing problems which would have to be overcome. "For one thing, we'd be talking about a lot of wire, and I have no idea what his wire-drawing capacity might be. And I'm fairly certain that it would have to be wrapped really tightly, tighter than we can manage with muscle power, which is going to require his mechanics to figure out how to do it using water power. If they can't do it with what they have now, though, I'm sure they can figure out how to build whatever they need to build in order to build whatever they need in order to do it!"
He wheeled back to the wall of slate, chalk clattering as he wrote furiously. Then he spun back around to Merlin just as quickly, pointing at him with the piece of chalk.
"I don't believe for a minute that you 'just happened' to think of this, Seijin Merlin." It could have been accusing, but it wasn't. "On the other hand, I'm not going to ask any more questions today. I've got the oddest feeling that if I were to do that, we'd find ourselves getting into explanations you'd really rather not make."
Merlin managed to keep his expression under control. It wasn't the first time one of Seamount's comments had headed in the same direction, but this one was more explicit than most, and he decided not to mention a third problem the little commodore was about to encounter with rifled guns. The fuse system he'd worked out for his smoothbore shells would work just fine, relying on flash for the original ignition. But sticking that sort of fuse design onto the nose of a rifled round was likely to prove more problematical. Since a rifled shell was always going to land nose-first, a nose-mounted fuse would tend to be crushed on impact, or else driven back into the shell. In the first case, the shell probably wouldn't detonate at all; in the second case, it would detonate effectively instantaneously, before it had time to penetrate sufficiently into the target.