The Mahndrayn carriage was more practical than some of his other ideas, although his spring-driven recoil mechanism would probably work for lighter pieces. (Another design, for coastal artillery, using counterweights in a deep pit under the gun platform had proved practical even for the heaviest cannon, although the system would have been totally unworkable for a naval mounting.) As far as the recuperator was concerned, however, Rahzwail had profited in his development of Mahndrayn’s original sketches by consulting with the Royal College. Doctor Mahklyn had been able to nudge him gently past a couple of obstacles, but the vast majority of the work was his and Hainai’s original work, with substantial contributions from the College’s Doctor Vyrnyr. Merlin had found himself tempted to step in and push the project more than once, but Rahzwail and Hainai were doing exactly what he needed Safeholdians to learn to do, and so he’d let them run with it.
Still, he thought now, we do have a few advantages Ahlfryd and the others don’t know about. For example, I feel strangely confident that Ehdwyrd’s artificers will solve that leakage problem before too much longer. I believe “Doctor Owl” will have a little something to say about that!
“If—or, rather, when—we get the leak problem licked, we’ll have an effective recoil absorbing system,” Seamount continued, “and if we can manage that, I feel confident we’ll be able to produce the ‘pedestal mounts’ at least for lighter pieces.” He glanced at Merlin with a half smile as he used the term Merlin had coined. “For the heavier pieces, we’re still going to need something more massive, but I think the pivot mounts Fhranklyn and Master Howsmyn have been working on should prove practical. Frankly, one of the things that’s bothered me the most has been the need to integrate some sort of capture mechanism to latch the gun in the fully recoiled position for loading. It works fine with Urvyn’s counterweight system for the shore batteries, but I’m less comfortable with it for the recuperator. It’s an added complication and another potential failure point in the entire system, not to mention significantly increasing strain—or, at least, the period of maximum stress—on the pneumatic cylinder. But we have to bring the muzzle back inboard and keep it there if we’re going to reload it. Or”—he looked back up from his notes suddenly, his eyes sharp—“that’s been our working assumption from the time Urvyn and I started on the project. Now, however, Ahldahs and Fhranklyn have come up with a completely new suggestion.”
“New suggestion?” Rock Point cocked his head at Seamount and Rahzwail. “They do seem to come rather fast and furious around your lot, Ahlfryd. Is this another one I’d rather not get too close to on the proving ground?”
“It should work fine, Sir,” Seamount said reassuringly. “In theory, at least.”
“I could’ve gone all month without that little qualifier,” Rock Point said dryly. “I seem to remember a few other qualifiers which led to loud, noisy explosions.”
“But most of them’ve worked out in the end, Sir.”
“Including that flamethrower notion of yours? Or the liquid incendiary shell fillings?” Rock Point inquired just a bit tartly.
“I did say most, not all, Sir.”
Rock Point eyed him coldly for a moment, then snorted.
“Yes, you did. And, yes, most of them have worked out … so far. So what has Captain Rahzwail come up with this time?”
“Ahldahs?” Seamount looked across the table at his assistant, and Captain Rahzwail squared his shoulders.
“The idea actually came to me from another of Commander Mahndrayn’s sketches, My Lord. When he was looking at ways to seal the breech of his rifle, he considered the possibility of using a threaded plug, one that would screw in and out and produce a tight seal that way. He adopted the solution he finally chose because it would take much longer to screw a breech plug all the way in and out, and also because he was concerned fouling would cement the plug in place. But the notion of a threaded breech plug or block stuck in my brain, and it occurred to me that the plug didn’t have to be completely threaded.”
“I beg your pardon?” Rock Point frowned, his expression intent.
“If we were to cut away a part of the threads, My Lord, so that the plug could slide all the way into position, then rotate through a half-turn or so and lock solidly into place, it would greatly reduce the time between shots.”
“I can see where that would be true,” Rock Point said slowly. “But with part of the threads cut away, it would be impossible to seal the breech, wouldn’t it? Especially with the sort of pressures a large caliber piece generates.”
“I agree entirely, My Lord, but the idea intrigued me, so I discussed it with Captain Saigyl and with Admiral Seamount. We were throwing the idea back and forth last month, when Captain Saigyl pointed out the way in which Commander Mahndrayn used the felt bases of his cartridges to seal the breech of his rifle. Obviously, the pressures are much lower in a rifle, but Captain Saigyl wondered what would happen if we substituted a ring—a washer, if you will—of something else.”
Rahzwail looked expectantly at Rock Point, who nodded thoughtfully. Safeholdian plumbing had developed sealing washers and gaskets made out of several materials, including rubber, many of which were suitable for working with remarkably heavy pressures, so it was scarcely surprising that the concept should have suggested itself to Saigyl. Or scarcely surprising in Charis, at any rate.
“And just what sort of material did Captain Saigyl have in mind for his washer?” Rock Point asked after a moment.
“Stone wool, My Lord.”
“I see.”
Rock Point glanced down the length of the table to meet Merlin’s eyes. Stone wool was the Safeholdian term for asbestos, whose insulating properties and resistance to heat had been known since the Creation. Its use had been ringed around with warnings in the Book of Bédard and the Book of Pasquale, but it hadn’t been outright prohibited. Pasquale had declared an anathema against any form of asbestos other than chrysotile, hence the term “stone wool” from the whiteness of the material. Merlin wasn’t certain why he hadn’t banned it, as well. Admittedly, chrysotile was far less dangerous than the others, especially with the handling restrictions Pasquale had imposed, but long-term exposure to its fibers were scarcely beneficial to one’s health. Probably, he’d decided, it was because the archangels had managed to convince themselves the Proscriptions of Jwo-jeng had permanently eliminated the possibility of industrialization on Safehold. The material was undeniably useful—it had been used for thousands of years, long before Old Earth’s industrial revolution—and Langhorne and his followers had apparently consoled themselves with the thought that the quantities a preindustrial society would use would be relatively benign.
Unfortunately for what they might have thought eight or nine centuries ago, however, Safehold in general and Charis in particular had been using more and more of it over the past hundred years or so … and especially in the last decade. There simply was no choice. Industrial works like Ehdwyrd Howsmyn’s needed a material with asbestos’ properties and didn’t have the capacity to produce any of the synthetics which had eventually replaced it on Old Earth. As a result, “stone wool” output was climbing by leaps and bounds, and despite all Howsmyn, the Crown, and the Church of Charis could do to enforce Pasquale’s handling restrictions, exposure to it was climbing as well. It wasn’t the only health hazard Charis’ innovators had been forced to embrace—the mercury being used in percussion primers was a case in point, as were the shafting and exposed drive belts involved in applying water power directly to machinery—but somehow asbestos bothered Merlin more than many of the others.
Which didn’t mean Rahzwail and Saigyl weren’t on to something. After all, “stone wool” was exactly the same material Charles de Bange, the father of practical breech-loading artillery designs on Old Earth, had used in his “obturator pad.”
“Have you conducted any actual trials yet, Captain?” Rock Point inquired.
“Only with a modified Mahndrayn rifle, My Lord. So far, it appears a gr
eased stone wool washer or pad should do the job, assuming enough pressure on the screw threads. I’ve asked Doctor Mahklyn and Doctor Vyrnyr to help us determine a way to calculate how long a breech plug would be required and how much of the threads we could safely cut away. Doctor Mahklyn’s of the opinion that he and Doctor Vyrnyr should be able to give us some rough working formulas within the next several five-days. In the meantime, Captain Saigyl’s consulting with Master Howsmyn about the feasibility of fabricating breech blocks to the necessary tolerances. We won’t know for certain whether or not it’s practical even to consider the approach until he’s had a chance to discuss it with Master Howsmyn’s artificers.”
Rock Point nodded again. High-pressure dynamics was an entirely new branch of study here on Safehold, but it was making considerable strides. Dahnel Vyrnyr at the Royal College had begun formulating the rules of pressure and gasses, but it was one of Ehdwyrd Howsmyn’s artificers who’d really started the process of examining pressure levels in artillery a year and a half ago when he proposed what had been called a “crush gauge” back on Old Earth. Essentially, it was a hollow-based device, consisting of a tube which contained a small, very strong piston and an open frame which contained a small cylinder of pure copper. The bottom of the gauge was threaded, and a hole was bored through the wall of a gun tube and tapped with matching threads. The gauge was then screwed into the hole to form an airtight seal, and when the gun was fired, the pressure entering the gauge through a tiny port in its hollow stem drove the piston upward. A strong steel screw at the top of the gauge prevented the copper cylinder from moving, which caused the piston to deform—“crush”—the hapless cylinder. By removing the cylinder and measuring it very precisely, then comparing the measurements to those of similar cylinders which had been deformed by known pressures, the pressure inside the gun tube could be determined within very close tolerances.
No one outside the Charisian Empire had ever even heard of the technique, and Howsmyn had cheated slightly. The numbers from the cubes which had been crushed to establish the original base index were derived from cubes Owl had crushed under far more precise and uniform pressures than Howsmyn’s own machinery was yet capable of producing. Not even his own artificers knew that, since Owl’s remotes had sneaked in and replaced the ones they’d crushed when no one was looking.
And it had been Urvyn Mahndrayn who’d invented the ballistic pendulum, the high admiral reminded himself sadly, suppressing a fresh stab of grief. He’d sketched out the basic concept for it on the back of an envelope one afternoon while waiting for a meeting at the Royal College, and Mahklyn and the rest of the faculty had been working out the details—and the math—to make it work by the next morning. Between the crush gauge’s ability to accurately measure bore pressures and the ballistic pendulum’s ability to accurately and consistently measure projectile velocities, the science of ballistics was off to a rousing, brawling start, he told himself with a deep, warm sense of satisfaction, and he suspected Mahndrayn would have been just as fiercely pleased by the knowledge as he was.
“In the meantime, however,” Seamount put in, “Ahldahs has come up with a fallback position in case it turns out Master Howsmyn can’t promise us the necessary precision in manufacturing the screw blocks. It’s not as satisfactory a breech closure in a lot of ways, but it should work. Essentially, it’s a completely separate breech plug fitted with a copper washer lapped over a compressible layer of stone wool. An external screw clamps it in place with enough force to give a seal which has proven gas-tight in all of our small-arms tests. I don’t like it as much as I do this ‘interrupted screw’ approach, mostly because it will impose a much slower rate of fire, but also because I suspect it would be more fragile, more subject to external damage and breakage. Between the two, however, I think I can feel confident in proposing the adoption of breech-loading for our new generation of rifled artillery.”
“I see,” Rock Point repeated, and glanced at Merlin again. The seijin looked back steadily, then nodded ever so imperceptibly. “All right, Ahlfryd,” the high admiral said then. “It sounds to me like you and your pet geniuses are onto something yet again. And I’m sure that between you and Master Howsmyn, you will be able to make it work.”
Merlin’s expression was admirably grave. He, too, was sure they’d be able to make it work, especially since Howsmyn had access to detailed plans of de Bange’s original design, including the “mushroom,” the rounded “nose cone” at the head of the breech block. It was actually the most ingenious part of the entire concept in many ways, because when the gun fired, the mushroom was driven to the rear, compressing the asbestos “washer,” squeezing it so that it expanded outward to seal the breech completely. And because the mushroom was driven by the firing chamber pressure, the tightness of the seal automatically adjusted to different weights of charge. Merlin had no doubt that when Howsmyn sat down with Saigyl to look at his drawings, the industrialist would experience another of those intuitive inspirations for which he had become known and start enthusiastically sketching in ideas of his own.
“All right, now that that’s out of the way, what about this other problem you wanted to discuss?” the high admiral continued. “Something about bore pressures and combustion rates?”
“Yes, Sir,” Seamount replied in a distinctly less cheerful tone. “I’m afraid we won’t be able to get as much benefit out of some of the new advances as I’d hoped.”
“Why not?”
“Well, Ahldahs and Commander Malkaihy and I have been going back over the results of Urvyn’s artillery tests. We’ve repeated several of his firings using the new crush gauges to measure bore pressures and the pendulum to measure velocities, and they’ve confirmed something we already suspected. We’d hoped we could increase shot velocities by increasing barrel length, but it turns out we can’t.”
“Why not?” Rock Point repeated.
“Essentially, My Lord, the powder burns too quickly,” Rahzwail said. “It gives all its propulsive power in a single, sharp kick the instant that the charge fires; with a longer barrel, we actually start losing some of that initial velocity due to friction between the projectile and the inside of the gun tube. Looking at the pressure gauges, we’ve concluded that a great deal of the powder is transformed into smoke—solid particles and soot—rather than the combustion gases that actually drive the projectile. Corning the powder clearly helps in that regard, given how the particulate mass is reduced and how much more of the powder is actually burned before it’s ejected from the muzzle, but there are still limits, and we seem to’ve reached them … for the moment, at least.
“Of course, that’s only part of the problem. The rifled pieces’ shells are much tighter fitting, which means they rub against the walls of the bore more than round shot do. That increases friction still further, which costs us even more velocity, and the rifling studs only make it worse. Frankly, I suspect the new ‘driving bands’ Master Howsmyn’s experimenting with will be even worse than the studded shells in that respect. I still think the advantages outweigh the problems, mind you, but there’s no denying there’ll be more than enough problems to keep us busy.”
“And that’s not the only difficulty we’re experiencing,” Seamount put in. “Among other things, Master Howsmyn’s new steels, especially now that he’s tried adding nickel to them, are even tougher and stronger than we expected. That’s wonderful news in most ways, but, unfortunately, it also means we can’t produce satisfactory armor- and stone-piercing shells out of them, after all. The shell walls will be too strong for gunpowder bursting charges to shatter properly if we make them out his new steels. At the moment, it looks like it’ll be wiser to restrict ourselves to cast-iron shells for the smoothbores and the wrought-iron shells he’s already developed for the rifled pieces.”
“They seem to’ve worked quite well in the Gulf of Tarot and at Iythria,” Rock Point said dryly.
“That they did, Sir. And they should still be quite effective against wooden ships a
nd light shore structures. But it’s only going to be a matter of time—and probably not a lot of it—before people begin designing shell-proof magazines for their fortresses, for example. Ten or twelve feet of earth, reinforced by a few feet of solid masonry, would most probably stop any of our present shells from penetrating, even from the angle-guns, and overhead protection for the batteries is also going to be high on fortress designers’ list of priorities once they begin to recognize the threat’s parameters. That’s why we’ve been concentrating on producing shells heavy enough to do what the bombardment ships did at Iythria to the next generation of forts. Or even, eventually, to penetrate someone else’s ironclad. Wrought iron isn’t going to be as effective for those uses, and it’s more likely to break up or shatter on impact than Master Howsmyn’s steel, especially with the quenching processes he’s been developing to harden the new shells’ noses. But if we can’t find some way to improve our gunpowder, there won’t be any point putting a bursting charge inside those shells. Basically, we’d be restricted to essentially the same solid shot we’ve always used—heavier, with better penetration qualities, but still a solid projectile rather than an exploding shell.”
“And have you and Captain Rahzwail had any thoughts about how that might be accomplished?” Rock Point asked.
“At the moment, all we’ve really come up with is the idea that we should find a way to increase the uniformity of the powder grains, My Lord,” Rahzwail replied. “It seems to me that if we could … compress the powder, make the individual grains denser, and possibly produce it in shapes that would increase the surface area, we ought to be able to retard the burning rate at least somewhat. That would mean combustion would take longer, and the projectile would be accelerated for a longer period, rather than beginning to lose velocity from friction. For that matter, if the grains were all a uniform size, we ought to get a more uniform burn rate from powder lot to powder lot, which would make for much more consistent ranges and trajectories for a given charge of powder. I suspect that pelletizing the powder we’re using in the new Mahndrayns would improve their muzzle velocity measurably, as well. And Commander Malkaihy’s also suggested we might find some ingredient or adulterant that could slow the combustion rate for artillery propellants still further. Since it’s the charcoal in the gunpowder that provides the actual fuel, we’re considering alternative types of charcoal that would burn more slowly, but we haven’t found one that would do the job yet.”