I just came into an old Winchester Model 70 with a 26 inch long barrel. This barrel is chambered for the 240 Gibbs cartridge. I was wondering what kind of velocities I might be able to attain safely from this cartridge? I did see some ballistics in a very old P.O. Ackley handbook but was wondering if any one has read anything or tried some of the newer powders ? Any info would be greatly appreciated.

I shoot both the 240 Gibbs and a new version called a 6mm minicoop which is based upon a 257Roberts AI case with the shoulder moved forward. The 240 is over bore capacity but I would not hesitate to use any load data for the 6mmX06 as a starting point. Even using data
for the 25-06 as a starting point. H 4350and H4831sc and slower powders seem to work best.

http://shootersforum.com/showthread.htm?t=9284

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I wonder if I will get the published velocities for the 6MM-06 or less velocities due to the much larger internal capacity/volume of the 240 Gibbs case. Less pressure ,less velocity ? Then work my way up. If i can get 3,700 fps with a 75 grain then i guess its worth all the case fireforming work. Whats your guess as to velocity ?

With a 40 degree ackley should the velocity was notibly less than the standard 06. My guess with a shoulder angle at 30 degrees you will reach your desired velocity.

Every barrel,throat and chamber is different so I would feel comfortable thinking that you can exceed the 6X284, just not sure by how much. 3600fps+?

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