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What is acceptable velocity variation

 
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  #22  
Old 03-13-2013, 01:11 AM
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Location: deer park, wa 99006
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Re: What is acceptable velocity variation

One way to check your ammo is shoot a group at 300,400,or500 yards and see what your vertical spread is. Use a steady rest like the one you mentioned and see if your group is close to level means speeds are good,tall groups means wide velocity spread. Course this also will depend on your shooting skills but should give you an idea of consistency in your ammo. Typically I look for no taller than group is wide. Good luck hope this helps
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  #23  
Old 03-13-2013, 07:25 AM
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Re: What is acceptable velocity variation

One thing will cause all bullets leaving at the same velocity to have some vertical stringing. All bullets don't have the same BC when fired. The slight unbalance they all have causes them to wobble a bit in flight. The more they're unbalanced and wobble, the more drag they have and the more they'll drop 'cause they have lower ballistic coefficents.

One thing will cause bullets leaving at several velocities to have near zero verticle stringing. Bullets leaving the muzzle on its way up and close to maximum angle of barrel whip will be compensated for their velocity. Slower ones leave later in the upswing and depart at a slightly greater angle. Faster ones leave sooner at slightly lower angles.

Therefore, the amount of vertical shot stringing way down range may not directly reflect muzzle velocity spread. I've shot a few dozen rounds through chronographs at 1000 yard targets and noticed faster ones do not always strike higher nor slower ones always strike lower. Sometimes the results are reversed. And the velocity spread versus drop as calculated by ballistic software doesn't match actual firing results.

And vertical shot stringing at any range also includes the variables of the rifle and shooter.
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  #24  
Old 03-13-2013, 10:12 PM
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Re: What is acceptable velocity variation

Quote:
Originally Posted by Craig1972 View Post
Thank you very much. I am using a Shooting Chrony Alpha Master, it's pretty good. So I will concentrate on shooting ten shots through it, get the average and use that in my ballistics calculations. I won't worry so much about the Velocity Variation for now until i start reloading. I'll also shoot from a Lead Sled and hope the Federal ammo is somewhat constant. I really am looking forward to the day I can start reloading.
I know it is tempting to start going to a lead sled and bench but make sure after you get a load nailed down you don't keep shooting it that way and expect your results to be the same in the field. Practice in a way that is more consistent to how you might actually use the firearm. As some have mentioned you could see variations depending how the gun is held. You have to train to do things the same way every time. I've noticed some difference depending on how I'm behind the gun or at least I think so. Need more testing to be for sure on that. You may also want to keep your data around and combine it with other samples as well. An optical chrony can somtimes be sensitive to lighting conditions. You might not always see the same readings from the same load on different days so keep that in mind. That crony may get you close on your ballistics calcs but only the actual shot counts. The physics won't lie
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