Anyone have experience with the .270 win improved? What kind of velocity increase can be expected with the improved chamber over standard .270 win? How about some load data?

OTTO - I've never shot one myself, but done a few for customers. They reported about 150fps increase in velocity with 130s and 140s. All of them really liked the cartridge. All of them were avid shooters and thought it was a good chambering.

No doubt that a .270 Improved (Ackley style) will afford a bit more case capacity and velocity potential, but the real increase in velocity experienced in most conversions is due to the owner expecting more and therefore loading heavier until he achieves what he expects. At the same PRESSURE as the parent case, a .270 Improved would likely afford only 50 or 75 fps increase.

If your goal is higher velocity (and not case life or whatever other benefits are said to be afforded by an Improved chamber), you would do well to go to something like the Gibbs version, which actually utilizes more of the length of the case in added case capacity by moving the neck forward. The disadvantage with the Gibbs or similar design is that factory loads cannot be used to fireform*; the advantage is that you do get a more significant increase in case capacity as compared to the Improved version, and a proportional increase in velocity potential.

*Some shooters of these chamberings do use standard cases to fireform by seating the bullet so long that it headspaces the round by engaging the lands. This method will work, but it requires care not to overload and spike pressures. A better method is to start with something like .30-06 and size down the neck only enough that the case headspaces on the "false" shoulder.

[ 01-20-2003, 21:15: Message edited by: Stonecreek ]