It's likely that Grantville's machinists have heard of autofrettage. However, the autofrettage pressure must be much higher than the working pressure, which, for a cannon, is very high already. Autofrettage is typically used when pressures exceed 15,000 psi for brief periods of time, and so you must be able to achieve a higher pressure hydraulically.

Canon. In canon, the ironclad's main guns use Schedule 160 12" pipe as liners, wrapped with steel wire salvaged from the coal mine. ( 1633Chap. 4). That, of course, is heavily dependent on twentieth-century materials. Should steel wire become unavailable, the backup plan is to cast bronze reinforcements around the tubes. I imagine that if there were no steel tubes, they would use cast iron.

Quality Control

A newly-cast gun barrel might have cracks and cavities (Hoskins 42). Before a gun was accepted (and paid for) by the military, it was tested. The British proofed guns by loading them with a double charge, and setting it off. The gun was then examined for cracks; this included filling it with water to see if it leaked. (Lavery 84). The gun would also be examined, usually visually, for the correctness of the bore diameter and the trueness of the bore. Note that if the bore droops, or bows to the side, this will impede the escape of the ball, and thus increase the pressure that the barrel must withstand (Hoskins 65).

Flaws may develop (or worsen) as a result of use (or misuse). Firing the gun too rapidly so that it overheats, overcharging the gun, and ramming the gun too hard all can create problems. Bronze has the great advantage that it tends to "crack and bulge before it bursts," unlike iron. (Id.).

Now let's discuss the Gribeauval system, which gave the French the best artillery in late-eighteenth-century Europe. Much attention was given to tightening the manufacturing tolerances for both the bore and for the cannon balls it fired. Rather than merely judge by eye whether the bore was dimensionally correct, the Gribeauvalist inspectors used a caliper gauge to measure the diameter to within 0.025 mm. (Alder 150).

In canon, Grantville's machine shops quickly demonstrated that they could do even better. Early in the new time line, Ollie Reardon manufactures new three-pounder cannon for Gustav Adolf. The metal is soft bronze, in which he drills out the bore on a lathe. He notes that ideally the finish cut would be with a reamer. (Flint, 1632, chapter 46). Whether reamed or not, the final product impresses Torstensson, Gustav's Chief of Artillery: "Those bores are perfectly identical!" In response, Rebecca shows him a micrometer, and explains that it has an accuracy of 1/1000th of an inch (one mil). (chapter 47).

Gun Popularity

Table 1–3 shows that even in Elizabethan times, there was a trend toward heavier armament:

I don't have a bronze vs. iron breakdown for 1585, but in 1592, naval guns were 79 % bronze. (Walton 220). Thus, there was also a trend toward replacing bronze with cast iron.

This information is still relevant as of RoF; both ships and guns typically remained in service for several decades. The British warships in active service in 1631 included the British Bear(40 guns, 1580), Adventure(26 guns, 1594), Warspite(32, 1596), Nonsuch(32, 1605), and Assurance(34, 1605). As for guns, on the Portuguese Santissimo Sacramento(launched probably in 1653; sunk 1668), the bronze guns are dated, either explicitly by the caster, or implicitly by design. Nine were cast before 1600. Eleven, between 1600 and 1650. Five were just identified as mid-1600s, and one was 1653. (Guilmartin). On the Kronan(sank 1676), one gun was cast in 1514 (Hoskins 18).

It would of course be nice to have comprehensive data for a date closer to the RoF (1631). I have found the Royal Ordinance Inventory for 1637 (Collins), but that's for the army. While the Royal Ordinance also supplied the navy, the latter would have requisitioned a different assortment.

What I can provide is data for individual ships; table 1–4 attempts to correct the usual British bias by providing some French, Danish, Swedish and Dutch examples.

By way of comparison, the principal Napoleonic battleship, the "74", usually had 28x32pdr, 28x18pdr, 18x9pdr. (Lavery 121).

In the table, I introduce the metric "broadside weight," the total weight of shot that can be fired at one time. This is probably a better measure of the power of a warship than just the nominal number of guns.

From a ship design standpoint, another important metric is the ratio of that broadside weight (pounds) to the ship displacement (tonnes); for the Swedish navy, it was around 0.4 in the 1630s, but increased to 0.75 in 1671. (Glete 571). In that year, the Kronancarried an armament of about 180 tonnes, 8 % of its 2,300 tonne displacement. (572).

Horizontal Distribution of Guns

We may recognize three basic gun arrangements: predominantly frontal; predominantly broadside; and turreted. The Mediterranean galleys are in the first category. One of the more powerful of the Venetian galleys at Lepanto (1571) might have a 52–55 pound full cannon, flanked by an inner pair of 12-pounders and an outer pair of 6-pounders. And it could have a second deck, carrying swivel guns, as was certainly the case for the larger Spanish galleys. (Guilmartin, 322-3). In the eighteenth and nineteenth centuries one could also find heavy frontal armament in certain specialized warships, bomb ketches and rocket ships. In the twentieth century, we have a similar arrangement on torpedo boats and missile boats. And attack submarines may be said to have a spinal armament, firing torpedoes from bow or stern.

Most warships of the late-sixteenth through mid-nineteenth centuries were designed to deliver powerful broadsides, but had rather weak bow and stern armament. Once the "line ahead" formation and related tactics, which lent themselves to delivering broadsides, were developed in the mid-seventeenth century, this was particularly true of capital ships. A frigate or lesser vessel was more likely to have chase guns.

Despite the importance of the broadside, seventeenth-century French warships tended to have relatively powerful bow and stern armament, because they were used in the Mediterranean against galleys. This required some adjustment in the hull to provide a good firing arc. (Langstrom 167). In general, since the number of bow and stern guns was limited by space, those tended to be the ones with the best range and accuracy. (ChapelleHASN 12).

It's perhaps worth noting that warship designers of the second half of the nineteenth century were "ram-crazy"; this in turn led to an undue emphasis on frontal firepower for steam-powered ironclads.

For a ship with broadside armament, the length determines how many guns it can carry per deck. Length was limited by structural concerns; local inequalities of weight and buoyancy would cause it to droop in the center (hogging) or sometimes at the ends (sagging). These in turn imposed strains on the hull; they were proportional to the square of the length. Wooden-hulled warships consequently weren't much longer than 200 feet; a British first rate of the 1745 Establishment was 179 feet at the gun deck. (Ireland 41).

Of course, the number of guns carried on a deck of particular length depended on the spacing between the gunports, and how close they came to the bow or stern. On the Dauphin Royal(1735), 74 guns, there were 13 ports to a side, the foremost about 18 feet from the stem and the aftmost about 10 feet from the stern. The port width was 2'10" and the distance between ports (edge-edge) was 7'7". (du Monceau 4).