Originally Posted by huckjare
I have a CZ 550 tactical in .308. I am planning on rebarreling it in a .260. I have heard that with the .308 and the .260 barrel length (from 20'' to 26'') doesn't make a difference because all the powder is burned before it reaches 20'' mark. My question is, Is this true? If I can get away with a 20'' barrel and save the weight from a 26'' I would love it, but I don't know if this would hold up. There are a lot of 20'' .308s out there, but do they lose velocity. I am more interested in what a .260 would do. If anyone has experience with this please let me know. Thanks.
A bullet does not stop accelerating in the barrel the at the instant the propellant is 100% burned. It only stops accelerating when the force on the bullet from the hot propellant gas drops below the forces on the bullet from bore friction and air pressure in front of the bullet. The only place that happens is when shooting small capacity cartridges from long barrels,, usually subsonics. . Larger cases with smaller bores do need longer barrel lengths to efficiently reach their practical velocity capabilities, but sometimes it's desirable to give up some performance for a more compact firearm. That "wasted" energy can still be used with a muzzle brake to reduce felt recoil in a lightweight rifle.
Here's an comparison of 260 Rem barrel length using a Quickload simulation. Shooting the 123 Scenar (l low drag bullet) from a 26" or a 20" barrel using 42.8 grains of H4350 which is a 100% case fill and about a 90% SAAMI max load, a 26" barrel gives 2959 fps and a 20" barrel gives 2781 fps. Muzzle pressures are 8940 and 12072 psi respectively.
At sea level the range to where the 123 Scenar will reach 1300 fps with the 26" barrel is 1220 yards. Using a 20" barrel gives the same performance if shot from 100 yards less. (the 2959 fps bullet drops to 2781 fps in the first 100 yards.
I won't comment on the suitable hunting range of either barrel length. There are too many variables including the animal, the wind conditions, and the shooter's skill.
In the above example according to Quickload the powder is 97.44% burned in the 20" barrel, 98.99% burned in the 26" barrel.