Pistol barrels range from 2" to 12", and almost every increment in between. Longer barrels increase accuracy, shorter barrels make for more compactness.
Shorter barrels = less MV
Because it is a pistol, not a rifle.
e-gunparts.com, gunbroker.com, or auctionarms.com might have them.
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A small pistol / Derringer w/ rotating barrels, imported. Mostly brass colored w/ black barrel 2 shot cap.
In almost all of them, yes. There have been a very few rare 45s that were made with smoothbore barrels to fire shot cartridges.
300 or so
Depends on the maker. Some gun barrels are the finest quality type 4140 chrome moly or 416 stainless steel with button rifling. Hi-Point pistol frames are made from a high-impact polymer and barrels are from an alloy stainless steel.
Rather pricy. About $575-$775, depending on condition- more if you have both barrels (they came with 2)
From the face of the slide to the muzzle. Insert a dowel near the diameter of the bore until it contacts the face of the slide, mark the dowel at the muzzle, withdraw, measure.
It really boils down to the quality of materials and construction which goes into the barrel. Some barrels will last longer than the lifetime of you and your children. Some will not.