The problem with the Crossbow is that, while awesome, it just doesn't fit in Steve's world. The Crossbow was originally invented because archers took for freeking ever to train, were paid as specialists rather than as grunts, and in general were a very valuable resource. The Crossbow was something any grunt with six weeks of training could aim in more or less the right direction and let fly at a mass of bodies (also known as a formation) and hope to have some effect.
In fact, one could say that the musket was the improvement over the Crossbow, rather than the Longbow, since a Longbow still had a greater rate of fire, greater range, and (with the Grey Goose cloth yard shaft) greater penetration. The musket, however, could be fired en masse by impressed/conscripted soldiers with minimal training. It was a quantity over quality thing.
It wasn't until the Winchester Repeating Rifle or the Colt Peacemaker that firearms had any qualitative advantage over a good archer.
However, if you wish to create a gun that would fit in Steve's world, we're going to probably be looking at something like the Kentucky Long Rifle, and do a bit of... creative anachronism.
So, we're looking at a flintlock in the .45 caliber range. Now for the anachronism. We're going to be taking a bit of an idea from the paper cartridge, only without the fulminated mercury. Basically, you carefully measure your powder into a piece of paper, put your shot into it, fold it up and twist it. When you need to reload, you rip off the top with your teeth, pour in the powder, use the paper as wadding, and ram the shot home. This gives Steve the reliability and consistency of burn needed for true marksmanship with a rifle, and without the fumbling around with a powder horn.
Technically, it's only an anachronism because while such paper cartridges were around as early as 1600, perhaps even earlier, they were not often used with rifles, because the entire cartridges were dropped into a musket. So you'd have to rip it off and pour it in to get the advantage of the rifling. This technique was not used en masse until the Civil War era. But hey, if Daniel Boone can do it, so can Steve!
Therefore, here's what we're looking at, mechanics-wise:
To make the shot requires a ball, a gunpowder, and a paper. It's not a shapeless recipe, so you have to do it in a crafting table, to represent the fact that you're carefully measuring the gunpowder before hand rather than being a 'field expediency'. The ball is cast in a smeltery, one lead ingot will cast eight balls. Historically, lead was used because it was malleable (was able to be rammed into the rifling and fit the grooves) and because you could melt it into the cast over a campfire. Since we're still using a fairly primitive means of using rifling, no other metal will really be able to engage the rifling, so only lead will do.
Reloading the rifle requires a combine in your crafting square (shapeless) of your rifle, your shot, and your ramrod. This represents the additional time it took to reload a rifle over a musket.
Now, we need a new table, in addition to the Tool Forge. This is the Gunsmithing Table, and is used to construct the flintlock mechanism. Unlike typical TiCo mechanics, the flintlock mechanism is made on an anvil rather than cast, so we're going to be crafting much like a typical wooden pattern, using iron to make the thing. The barrel is cast, then you need to bore it at the gunsmithing table to give it the rifling. The stock is effectively the 'handle', and affects durability as any handle material would.
The combine for the gun must be done at the Tool Forge (not station). Stock + Flintlock Mechanism + Rifled Barrel = gun.
It should probably start out at 10 hearts, however should not gain any bonuses from modifiers, including modifiers to ammunition. Therefore eventually a bow CAN be a better weapon, but it requires a lot of modifying and resource investment to do.
