What is acceptable velocity variation

[rinodods]

I could be wrong, but won't ST DEV always be less than ES?

I'm glad I wasn't the only one scratching my head here. I think we may be way too into the numbers if we noticed that.

 

[Craig1972]

If most chronographs give you Standard Deviation, (and unfortunately not Velocity Variation), why don't most Ballistic Calculators/Aps ask for Standard Deviation? Thank you.

 

[rinodods]

If most chronographs give you Standard Deviation, (and unfortunately not Velocity Variation), why don't most Ballistic Calculators/Aps ask for Standard Deviation? Thank you.

Honestly if your crony gives you SD it will also give you ES. Kind of depends on who you talk to as to which if more meaningful. I tend to pay more attention to SD. ES does give you the worst case example though. Along with ES and SD your chrony will likely give you the average speed which is probably what most are going to use in their software.

 

[jasent]

Honestly if your crony gives you SD it will also give you ES. Kind of depends on who you talk to as to which if more meaningful. I tend to pay more attention to SD. ES does give you the worst case example though. Along with ES and SD your chrony will likely give you the average speed which is probably what most are going to use in their software.

mine gives both but I normally use the avrege speed for calculating. Tho I'm normally not happy with a load till es is below 20 consistently. Many times if my vertical spread is more than .5 moa than my chrono also shows a high es,sd. Tho the load i mentioned earlier often has .25moa vertical spread at all ranges. It does not buck the wind very well with the little bullets but I've been getting pretty use to how it drifts. Many times I've noticed my speeds may not track with data but it must lie consistent cause it predicts vertical spread well and normally when it's wrong its 1/2 moa or less. Could be that +/- 5% accuracy they talked about in the Manuel.

 

[Craig1972]

"Honestly if your crony gives you SD it will also give you ES" thank you guys. I will double check my Chrony and see if it does in fact give "ES" (which i didn't realize was Velocity Variation. Getting my Velocit Variation down from 45 to 20 might be tough since i'm using Federal Premium ammunition (165 grain GameKing for my .308) I heard if i am bench shooting it without a Lead Sled it may vary so much because of the variation of how i'm holding the rifle. but don't oi want to get my velocity average and variation the same way i'd be shooting my rifle in the wild and not with a Lead Sled?

 

[jasent]

Yes but I dont believe reacting to recoil can change velocity that much. Guess ill have to test this theory. I've always been told recoil starts when the bullet exits the barrel not at ignition. Tho ignition and bullet exiting are only thousandths of a sec apart so.... Also have to remember that chrono's are not perfect and many are only accurate to +/- 5% at 3000fps that can be +15/-15 fps each shot,also if your ammo is sitting in the sun waiting to get shot its warming up as well which will change speeds or if your action is warm or hot and your taking your time making sure your doing your part as they say it may also be warming it up. Combine that with normal +/- of the chrono and that could easily be your 50fps spread. or your factory ammo is just not that constant.
I'm no expert! Jmo

 

[Craig1972]

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.

 

[jasent]

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

 

[Bart B]

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.

 

[rinodods]

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