Advanced mathmatics....


Well-Known Member
Nov 10, 2001
Hello again!
OK, you're going to love this one. Somehow, it has to be possible to describe the overbore charactoristics of a cartridge and the inches of barrel required to burn the volume of powder it contains. For instance, I read an article some time ago where the author took an 8 x 57 with a 29" barrel, fired it over a chono, recorded the velocity, cut an inch off the barrel and repeated the process again. In the end, the 8 x 57 gained velocity with every shortening untill it got to about 22" or so and then it started to loose velocity. As I recall, it was around 18" when it had slowed to the same velocity that it started out with.
Somehow, there is a formula that states " when X volume of powder is burned in Y diameter bore with Z weight projectile in front of it then W length barrel is required to burn all of X powder without slowing the bullet due to excessive barrel length". This formula could also give an approximation of velocity decrease per inch of barrel removed.
Feel free to tell your friends at the local university about this one... I'm sure that for the right person, it's not that tough.
Thanks, Coyoter

Darryl Cassel

Well-Known Member
May 7, 2001

I too have read that article. The test was run many years ago and there was only ONE load (Bullet and Powder) used for this test.

I believe the load was made for the military rifle which had a shorter barrel to start with.

With the many powder and bullet combinations available today, I can assure you that for every inch of barrel above 22" a velocity gain of 25 to 50 Feet per second can be achived. At a point normally above 37", bullet drag becomes a factor (with the powders we have to work with) in the barrel and the velocity increase will slow down per inch. With even slower powder (if it was available to the civilian population) I believe the drag factor would be much less and the bullet increase could be more constant at longer barrel lengths.

Maybe someone would have a math. equation for this but, the exact formaula would be hard to construct because of all the powder burn rates and bullet combinations that can be used when sending a bullet down a barrel.
The equation would probably have to be for EACH load used in the test and at various barrel lengths.

For instance I have a friend who has the 338/378 with a 30" barrel. The fastest velocity he can achieve with that barrel and the 300 gr Sierra is 3020 FPS. Using the SAME powder charge and bullet load my 37" 338/416 will maintain 3200fps
I can tailor my rifle to shoot 3310 FPS with the 300 gr bullet if I don't care about loading my brass more then two times.

We have experimented over the years with the longer barrels and have found that the larger overbore cartridges need the extended length barrels and slower powders to cause a bullet velocity increase that is needed for longrange hunting.
A 22" barrel will not do it when shooting at extended range.

Darryl Cassel

[ 11-14-2001: Message edited by: Darryl Cassel ]

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