Thread: 25-06 velocity
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Old September 10, 2012, 07:50 AM   #9
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Join Date: November 8, 2007
Posts: 2,001
Getting back to the OP's question about WHY he isn't getting to 3000 fps:

The .257" bullets have only 86% of the base area of your .277" bullets. So, to get the same acceleration with the same pressure-vs-time curve in the same barrel length, you would want to have a .257" bullet that is 86% of 130 grains, which is 112 grains.

But, things aren't quite that simple, because you don't actually get the same pressure-vs-time curve in a .25-06 that you get in a .270 (i.e., a .27-06). The volume of the barrel is smaller in the smaller caliber, while the volumes of the two cases are about the same. SO, the pressure remains higher in the .257" barrel than in the .277" barrel, and that helps make-up some of the difference. But, not quite as much as you would think, because it is really the PEAK pressure that is limiting, and the smaller bore makes the same powder charge produce a higher peak when bullet sectional densities are equal, and even higher yet when the bullet sectional density is higher. Thus, the .25-06 max load is not going to be quite as much of the SAME powder as the .270 load to keep peak pressures within the limit. But, that can be compensated with a slower powder.

In addition, you have an extra 2" of barrel length, so that should add something like 80-to-100 fps over an exact comparison.

So, yes, it is reasonable to expect similar MAXIMUM muzzle velocities.

BUT, you say you are loading for ACCURACY, rather than max velocity. In that situation, all bets are off with respect to whether one rifle is more accurate than another at max velocity. The longer barrel length will surely change the velocity sweet spot due to different barrel vibration harmonics and different barrel exit time for the bullet at a particular velocity.

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