Midst Toil And Tribulation – Snippet 38
“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 breach, 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 breach 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.”
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 could 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 pre-industrial 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 last century 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 was the shafting and exposed drive belts involved in applying waterpower 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 greased 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 Mahndrayan 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 breach 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.”