Steel
Adding a longer barrel to a gun can improve its accuracy by providing a longer sight radius and allowing for better bullet stabilization. It can also increase muzzle velocity, resulting in a flatter trajectory and potentially more energy upon impact. However, the overall improvement will depend on various factors such as the type of gun, ammunition used, and individual shooting skills.
Within limits, a longer barrel means a faster bullet. It is pushed by the expanding gasses from the fired cartridge for a longer time, and accelerates to a higher speed. A longer barrel will also mean a longer distance between the front and rear sight, permitting greater accuracy in aim.
No. the longer barrel will preform better.
Oxidation of the steel of a gun barrel.
Did marlin make a goose gun with a thirty nine inch barrel
See the link below
Any tube that is .175 in diameter.
The BSS
No
Lands and grooves are the portions inside the barrel that make up the rifling, which is a spiraling series of raised lines (lands) which put a spin on the projectile as it travels down the barrel. This stabilizes the projectile and allows longer range and better accuracy.
I do not personally, but yes, there is a single shot rifle that can have the rifle barrel replaced with a shotgun barrel.