barrel length and bore size

[degreen]

I was just thinking of doing a long range target rifle in 243 Winchester, and I am wondering if there is a rule of thumb between bore size and barrel length. What I am asking is can the barrel of a rifle chambered in 243 be longer than a rifle chambered in say .308 due to bore diameter. I am thinking smaller bore = less volume with same case capacity = longer barrel.

 

[hemiford]

You are exactly correct. Two cartridges with the same charge weight
need the same barrel volume to achieve the same expansion ratio.
Only then can you compare ballistics and pressure curves.
From this, it's clear that a smaller caliber needs a longer barrel.
Kind of a pet peeve of mine that some people have no problem
comparing a 308 with a 26" barrel to a 300RUM with a 26" barrel,
for example.

 

[Rich Coyle]

hemiford,

You could put a 10 foot barrel on a .308 and it will never compare with any .300 magnum.

 

[WildRose]

You are exactly correct. Two cartridges with the same charge weight
need the same barrel volume to achieve the same expansion ratio.
Only then can you compare ballistics and pressure curves.
From this, it's clear that a smaller caliber needs a longer barrel.
Kind of a pet peeve of mine that some people have no problem
comparing a 308 with a 26" barrel to a 300RUM with a 26" barrel,
for example.

There is no relationship between barrel length and caliber.

Optimal barrel length is based on case size, bullet weight, and desired velocity.

The longer the barrel the slower the powders you can use and get more velocity with less pressure giving you better barrel life due to reduced throat erosion.

20" and under is more than adequate for .308win and smaller cases with any powder.

Longer barrels and slower powders are what allow us to achieve high velocities with the larger cases in the "magnum" calibers.