Barrel Length

[Badshot10]

Does anyone know of a good program that plugging in the caliber, bullet length,bullet weight, twist, and powder that will provide the optimum barrel length.

For the that matter, the correct twist.

I desire to build a 243ACK built for 85-87 grain bullets.

Thanks

[bigbrother]

Don't know of a program that would tell you that. I'm assuming from the bullet weight, you're making a varmint gun?? The other thing to consider is total gun weight. If I'm thinking of building a varmint gun with that case capacity, shooting a light, high velocity bullet and wanted a gun to carry from the truck to a groundhog field I would go for a 27 to 28" barrel. If you're only shooting the 85 to 87g bullets, I think a 1-10 to be best. (This won't allow you to shoot the screamer 55-75g bullets though as the velocity and fast twist will probably blow up the bullets before they get to the target)

On the flip side, if I wanted to shoot this gun out to say 1000yds, I would be looking at shooting the 107g or 105g match bullets out of a 30 or 32" barrel with a 1-8 twist. Of course I would want this gun to weigh about 22 lbs or so (not one to carry around )

In general, think of it this way. The lighter the bullet, the slower the twist rate. Velocity plays a big role also though...the faster you can push a bullet (ie long barrel) the slower the twist rate you need to stabilize it. Twist rate will also affect the velocity of a particular bullet. In general (not always) a faster twist rate will shoot a little slower with the same bullet/load combination. All in all, I would consult with the smith that's building the gun as he knows more about what you're going to do with it and can recommed what he feels is best.

[Cossack]

There is a formula to determine twist rate. www.z-hat.com/twistrate.htm
No such thing I know of for barrel length, just guidelines. Largely depends on case capacity, caliber and how much you want to maximize performance of the powder used, velocity desired etc.