Originally Posted by
MistWolf
Heat isn't just about temperature, it's about the amount of heat the barrel has absorbed. Barrels with less mass reach higher temperatures because the heat is more concentrated. With the raised temperatures, the barrel is more susceptible to heat damage. Added to that is barrels of less mass and of the same length (assuming both are circular) have less surface with which to radiate heat.
If one were to shoot two barrels, one massing 1lbs and the other 2lbs, it would take more heat (more rounds fired) to bring the 2lbs barrel to a temperature of 200 degrees. With both barrels heated to 200 degrees, it would take the 2lbs barrel longer than the 1lbs barrel to cool to ambient temperatures because it's holding more heat.
However, if both barrels were subjected to the same amount of heat (measured in joules, BTUs or other unit of energy), the 2lbs barrel would have a lower temperature than the 1lbs barrel.
This does not mean the pencil barrel is not a good choice for a carbine. A light-weight fast handling carbine is a joy. It just means like everything else in life, barrel mass is a trade-off. In this case, I would choose the fast handling qualities of the light barrel over the thermal advantages of the heavy barrel.
Also, quality light-weight barrels are very accurate