It depends on what they're being aimed at, and also the point of reference.
No
colt
H&R and I believe Rossi have single shot rifles with interchangible barrels.
Heavy Barrel
Rifle Muskats Sub Mrines Rifle Barrels Cannons
You will need a gunsmith to know for sure.
rifle barrels may have a different external diameter. A rifle that is carried for hunting will usually have a "sporter" barrel- slender, to save weight. Target rifles will have more massive, stiffer barrels for accuracy. Those are "heavy" barreled rifles.
If you have the money, they can be made.
Rifle, handgun and shotgun can all have "long" barrels
How much Remington Armory 1918 bolt action rifle barrels are worth will depend on their condition, overall state and wear, and can range from $200 to about $800.
Because it is a pistol, not a rifle.
The angles of a trapezium add up to 360 degrees. Whether or not it is right angled is irrelevant.