The longer the barrel the further the shot, why is that?

A short stiff barrel is more accurate than a long, whippy barrel.

A longer barrel provides more velocity. This promotes accuracy at long ranges because the bullet is supersonic to a longer range. For rifle cartridges each additional inch of barrel adds roughly 20 to 40 feet per second in velocity depending on the cartridge used.

At 100 yards a rifle with a short barrel is just as accurate as a rifle with a long barrel. The bullet will stabilize just as well. The short barrel may be even more accurate because it is more rigid.

A longer barrel provides a longer sight radius when using iron sights which helps the shooter to shoot more accurately.

depends on if you are shooting slugs or buckshot. With a slug, the kind of bullet or slug you are using matters more than the length of the barrel. If you have a rifled barrel then you DONT want a rifled slug. I recommend a hornady sst slug for rifled barrels. If u have a smooth bore barrel then I would buy a rifled slug. You can tell the difference by taking your barrel off. Look through it into a light source and see if it has corkscrew lines down the inside of the barrel. If it does, it is a rifled barrel. If not it is obviously a smooth barrel. Slug barrels are used for big game such as deer, and are usually around 24 inches long. Small game barrels, typically used for squirrel, rabbits, cyotes, etc., are always longer and require modified or "choked" barrels. Usually around 28 or so inches. Use buckshot with these barrels. never good to shoot slugs through these because the bullet tends to travel different patterns every time. You can buy chokes for these which will keep your pattern "tighter" and give you more accuracy at a longer distance. When shooting a gun it is all about accuracy and having the right ammo with the right barrel. Distance means nothing if there is no accuracy behind it.

At one point in time, longer barrels were very common and desirable. The current trend seems to be shorter barrels. Longer barrels up to a point increase the velocity. Long thin barrels whip a lot more than short heavy barrels. If the thin barrels whip consistently they can be accurate. Stiff barrels tend to not fling the bullets around as much.

There's a persistent myth that a longer shotgun barrel will give you extended range compared to a shorter one. It isn't true. In rifles, a longer barrel does increase muzzle velocity a little, but it doesn't make a significant difference in range. Neither is a longer barrel necessarily more accurate than a shorter one.

basically, longer barrels to a extent = more velocity = less time in air and less time for the environment to effect the bullet's path = more accuracy.

but there's a limit, since the bullet will only gain velocity when it has sufficient pressure behind it pushing it, if the pressure lowers, the friction of the barrel will bleed off velocity, lessening accuracy, most rifles have barrels of 26-28" for a reason, it's the optimum length for those particular cartridges.

Longer barrels allow for more complete burning of the gunpowder, but there's a trade off. The longer the barrel, the more resistance, so extremely long barrels may be more accurate, but you may lose some distance. Everything's relative.

It does help with accuracy and stabalizes the bullet to maintain accuracy for longer range shots.