In the SAAMI tests with barrels from 22 to over 30 inches and bullets in the 2500 to 3000 fps range, muzzle velocity increased about 25 to 30 fps per inch of increased length. SAAMI's web site has documents on centerfire rifle cartridges documenting this.
Unless the barrels one uses to compare muzzle velocity have the exact chamber, bore and groove dimensions as well as firing pin and ammunition properties, the velocity numbers for each length will not be good for comparison.
Exactly how does one measure or calculate the "efficiency" of a load for a given barrel?
Dan Lilja did a test that involved starting with a 46" barrel and cutting the barrel 2 inches shorter
and re crowning after each test.
It is a very good article and well worth reading. Log on to his web site and find it in "Articles".
It shows the relationship with velocity and barrel length and the deference in short barrels and
long barrels also.
I don,t know if there is a good way to measure efficiency of any load except if it is consistently
faster or shows less pressure than listed loads. Also some barrels are a little faster than others
with the same loading and may skew any efficiency test.
For years I had heard that short fat cases were more efficient than longer cartridges with less body diameter. and when comparing a 7 WSM to a 7 rem mag I found that it took the same or less powder in the 7 rem mag to achieve the same velocity with the same bullet weight Even though
the effective barrel length in the 7 rem mag was shorter because the case is longer with the same overall barrel length.
The powder and primers were the same in both rifles.
As you said there are so many variables that I don,t think there is any way to accurately measure
efficiency.
Just my opinion.
J E CUSTOM
