Barrel length vs velocity

[Moe]

Whats a good general rule of thumb about velocity/barrel length: Lets use a 357 max as an example. If I get a certain velocity from a 10" barrel, will that velocity increase as the barrel does? I know it will, but how much per inch, and when will it stop. If I wanted a carbine in this caliber is there a certain length when no more speed will be achieved? How does this relate to other calibers also, lets say a 6mmTCU. I would think the maximum velocity of a 6mmTCU would be reached in a longer barrel than a 357 Max. I know this is rather vague but maybe someone can explain this to me. :roll:

[jhalcott]

HEY MOE,the general rule is the longer the barrel the faster the bullet! An awful lot of things affect this rule,powder type is one. The Olympic shooters found that a 19 inch .22 rf barrel was the best length for velocity.
Longer barrels actually slowed the bullet because the powder had reached it's maximum expansion at 19"'s. Hornady's manual says the 14" barrel in the 7tcu gains  about 150 to 200 fps on the same load in a 10". I think you will find similar results with the 6tcu. It is theoretical to build a barrel so long that the bullet runs out of steam and stops in the bore. It might be a mile or more in length though.
 As far as how much per inch velocity gain you get, most people say 75'/sec/inch.But I have seen as much difference in just changeing guns using the same load. Use a chronograph and work up to your most ACCURATE load. hECK,I've got loads that can only be used in COLD weather,and they don't get any more speed than the summer loads for the gun! :wink: