RE: Barrel length ques..
I don't think that a longer barrel in a scoped rifle makes it any more accurate. With iron sights the longer barrel usually means the sights are placed farther apart (longer sight radius) which makes it easier for the shooter to be more precise. But the rifle itself isn't any more accurate, it's just easier to aim precisely. As a case in point, there is a local guy that had the barrel of his scoped Remington M700 heavy barrel .223 cut down to 18", and it still fired 1/2MOA groups afterward. The velocity was much lower I'm sure, but it was a handy little coyote rifle as long as the shots aren't too far out.
I think that's what you're thinking about with pistols too. Barrel/slide length on a pistol has a big impact on how easy it is to aim with the sights, because a small increase/decrease in sight radius makes a big difference.
In reality, all else being equal, lengthening a barrel should make it less accurate because a longer barrel is more flexible and will vibrate with a higher amplitude than a shorter barrel of the same thickness, material and construction. But the differences are probably very small in terms of group sizes downrange.
As far as barrel length and velocity goes, a longer barrel is generally going to produce higher velocities. The gains or losses in velocity depend a great deal in the cartridge being fired. For instance, the velocity gained from lengthening a .22LR barrel from 18" to 22" is likely going to be very small. But the velocity gained by lengthening a 22-250's barrel from 22 to 24" can be significant (100+fps). Generally speaking, the higher the velocity of the cartridge the more velocity you'll gain or lose by changing barrel length. Longer barrels also are benificial to large capacity magnum cartridges that shoot slow burning powders. If you look around at the rifles offered by the various manufacturers, you'll notice that most of the non-magnum rifles have barrels 20-24" length, but the magnum rounds almost always have barrels 24" or longer. Anything less than 24" in most magnums means losing enough velocity that the magnum isn't ballistically that much better than a non-magnum of the same caliber, but with all the recoil, muzzle flash and noise of the magnum.
As far as longer being better, I quess it depends on what you want out of your rifle. Most varmint rifles chambered in the smaller high velocity calibers all use 26" heavy barrels to squeeze every little bit of practical performance out of the cartridge. But when you're shooting prarie dogs off a bench rest it really isn't a big deal to have 26" of barrel sticking out in front of you all the time. But for a deer rifle that you plan on toting around the woods, a 26" barrel might mean another 100-150fps of velocity, but the extra length and weight is going to make it less comfortable and easy to handle in the dense stuff. Like anything else, barrel length is really a trade-off. The best barrel length depends on what the purpose of the rifle is and the cartridge it's chambered for.
Mike
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