The dimensions you have now are more reasonable, yes, but have almost gone the opposite direction. The term “caliber” refers to the diameter of the barrel, from the “top” of the riflings, so essentially the diameter of the bullet itself. That means the new projectile you described would be .1 cal, rather than .22 cal. I think the dimensions you should use should also be for the case and bullet, rather than just the bullet. For instance, the ubiquitous 5.56x45mm NATO rounds actually describe two things. First, the bullet itself is 5.56 mm in diameter. Second, the case, not counting the tip of the bullet extending out of it, is 45 mm long. The dimensions for a .22 Long Rifle round, also called by its metric designation 5.6x15, would be a bullet of 5.6 mm diameter with a 15 mm long case.
The reason why mentioning the case size is important is because you can have a lot of different rounds with the same caliber. For instance, the M14 and AK-47 both fire 7.62 mm bullets, but you can't use the same ammunition for both guns. This is because the M14 fires 7.62x51 mm rounds, while the AK-47 uses 7.62x39 mm rounds. The whole gun, from the action to chamber to the ejection system, has to be designed for both the caliber and the case size.
The other thing to consider is that the muzzle velocity, 800 FPS, still seems awfully low, even for a smaller round. Consider the .22 LR. Its muzzle velocity is 1000-1800 FPS, depending on the grain (weight) of the bullet (lighter bullets having the lower muzzle velocities). Even the .50 Action Express, the round I mentioned in my last post, runs around 1300-1500 FPS. Compare that to rifle velocities: the ubiquitous .30-06 rifle round runs from 2500-2900 FPS and the .338 Lapua Mag that Aendri mentioned is around 2700-3300 FPS (in these cases it's the lighter rounds that have the high velocities).
The longer barrels of rifles, rather than pistols, can take advantage of those speeds, resulting in extremely long accurate ranges. But even the .22 LR is accurate out to around 150 yards, though this is when fired from a rifle. Most pistol rounds are accurate to between 100-200 yards. Beyond that, the bullet drop is too hard to compensate for, but the rounds will retain more than enough velocity to be lethal to ranges far beyond that.
So, for a few more things to consider:
- look at the size of the round again; if you do want to keep it that small, you might want to make it out of a material like Tungstun. Make it a small, high velocity penetrator instead of a more usual bullet. Otherwise, have it be in the more common pistol round sizes - there are a lot from about .35 to .45 caliber.
- consider upping the muzzle velocity; whether you keep the round small or make it larger, and especially if you make it a penetrator, speeds out to 1600-2000 FPS are quite reasonable
- increase the barrel length; now that the bullet isn't a 1 in x 2 in monster, with a huge case to go with it, you definitely can fit in a longer barrel than 3 in into a 10 in gun. The famous Desert Eagle is also a 10 in gun, and the average barrel length in it is about 6 inches.
- the rate of fire; I touched on it before, but 4 RPM really doesn't make sense. There's honestly no way a gas-operated, magazine fed weapon is going to cycle that slowly. With most pistols, definitely excepting machine pistols, the limitation on rate of fire is the speed with which you can pull the trigger and how quickly you run out of bullets, and how quickly you can reload.
- up the effective range; 100-200 yards is a good bet for most pistols. With fancy future-tech and a smaller caliber, high velocity round (maybe APFSDS – Armor Piercing Fin Stabilized Discarding Sabot?) the range could be even more.
I like guns and ballistics, so this is far from a chore. I'm far from an expert though; for that, on SARP at least, you'd have to talk to Doshii Jun, though I'm sure with all of the military folk here there are plenty of people to answer your questions. And again, this are all just suggestions/notions submitted for your consideration. The new stats are all perfectly correct and theoretically possible, but are just a little odd. Thus, feel free to ignore everything I've said, or just pick and choose what you will.
