Thread: Relationship Between Case Capacity and Muzzle Velocity

Greetings All,
One of my favourite authors for things gunny is John Barsness who writes for Handloader, Rifle and other magazines. Around 20 years ago John did some analysis of pressure tested load data and developed a rule which states:

Potential muzzle velocity increases (or decreases) at one fourth (25%) of case capacity in cases of the same bore diameter.

I have previously used this rule to predict possible velocity for the 6.5 x 55 at full pressure based on data for the 6.5 Creedmoor and 6.5 - 284. The long running thread on the 25-06 recently wound up talking about the .250 Savage and inevitably the Ackley Improved version was mentioned together with some of the claims of fabulous improvements in performance. I thought it might be useful to apply John's rule to see what it tells us.
The .250 Savage was introduced over 100 years ago claiming 3,000 feet per second for it's 87 grain projectile. A 100 grain projectile was considered but could not achieve the magic velocity with the powders then available. Pressure was kept at 45,000 CUP due the Model 99 action. Fast forward to today and modern powders allow velocity close to 3,000 fps at this pressure. The Ackley Improved increases the case capacity by about 14% based on what I have read which works out to an increase little over 100 fps or 3.5% of 3000 fps. So what about these claims of stupendous velocity increases you ask? For a start wildcatters don't use lever action rifles so in strong bolt action rifles and good cases pressure can be increased to about 50,000 CUP which allows an additional 100 fps or a little more. This gives us a possible 24 inch barrel velocity of approaching 3,200 fps. The wildcatters of yester year clearly went well past 50,000 CUP assuming they chronographed their loads at all.
Regards Grandpamac.