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How important are the chrono numbers to you?

Are you more concerned with SD or ES?

Do you have any insight on the juggling of powder and primer combo's to jock the numbers?

Teuf,
 

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Let me begin by saying that I prefer the lowest possible velocity spread. That's probably just an engineer's hangup, seeking repeatable results.

Extreme spread (ES) can be accentuated with minor glitches that are soon overcome. Standard deviation (SD), to my way of thinking, is more important. Put another way, suppose that you fire five shots at the following velocities: 3008, 2997, 3017, 3001 and 2550. The ES looks really bad, but the SD more nearly reflects that four of the five velocities were good.

To me one of the most important chronograph uses is to measure the velocity loss over a known distance, for example 100 yards. The velocity loss over the known distance allows you to determine the real ballistic coefficient (BC). If you know the already BC of the bullet, then you gain an insight into the bullet's stability. More yaw equals more drag. The yaw may be exaggerated by a high muzzle exit pressure, a twist problem, etc., but you know it's there thanks to the chrono.

If a bullet has a factory stated BC of .300 but your chrono leads you to conclude that the BC is .273, then you have learned valuable information. The ultimate advantage of finding the real BC is that you will be able to better predict the trajectory and windage of your bullet.

My knowledge of primer/powder combo's is more focused around research cannon. I don't feel that I can responsibly say off the top of my head, "Use 29 grains of XYZ powder with a Winchester magnum primer." Internal ballistics as it relates to pressure issues is a lot less predictable than most engineers would have you believe. Loads commercially sold are carefully developed by ammunition makers. Despite the advances in software, I am told that over 100,000 rounds of the new .17 rimfires were fired to prove their performance and safety.
 

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the safety in centerfire ammo is provided by the makers WUSSY LOADING everything. That's easy to see in comparing US ammo to European loads. Rimfire ammo is a different story. Centerfires were developed in the FIRST place because brass walks a VERY fine line between being "dentable" by the firing pin, and still strong enough to handle more than .22lr pressures. Autoloaders in rf are nearly always simple blowback, so the case's rupturing is a big deal. So are misfires in rds that cost 15-20c a shot. :)
 

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GBullet said:
Internal ballistics as it relates to pressure issues is a lot less predictable than most engineers would have you believe. Loads commercially sold are carefully developed by ammunition makers.
The Vihta Vuori model works quite well at predicting pressure/velocity figures up to a point. After that, expected results will differ widely from actual. Unfortunately, there is not really any way of knowing where that point actually is, without measuring both pressure and velocity. Usually the model is fine for predictions of pressure/velocity at least up to what is generally considered to be +P+ pressures. I use the model, but I also measure.

DC
 
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