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Bullet stabilization myth?

 
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  #15  
Old 04-07-2008, 04:23 PM
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Phorwath,

Your suggestion actually makes sense! At 100 yards the bullet is 1 moa (1 inch) but as fiftydriver said, it becomes very stable "falls asleep" at a further distance. So even though it's now 2.5 inches off at 500 yards, it is only .5 moa. I think that also fits within the parameters of what fiftydirver explained. Very interesting stuff...
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  #16  
Old 04-07-2008, 05:29 PM
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To really make things interesting, consider the effects this has on BC!!! That will really get you scratching your head.

I have seen many cases with bullets that have BC over .7 and especially those with BC in the .9 to 1 range drive to high velocity. The BC within the first 300-500 yards is often notically lower then the BC from 500 to 1000 yards or so. Then you often see the BC drop again in many instances past 1000 yards which can really make developing a drop chart a challange.

Exbal really allows you to tune your drop chart to your actual trajectory. Just a plug for Shawn Carlocks new video, get it and you will learn how this is done properly.

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  #17  
Old 04-07-2008, 05:37 PM
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Wow that's a headache... I have ordered Shawn's video. Loved it! I have watched it 4 times now. I had to make sure I was getting correct "station pressure" on my Kestrel by referrencing 0 altitude. That's a whole different argument. I changed my altitude reference to 0 on my Kestrel but still include altitude in exbal. Some argue otherwise. I will follow Shawn's video instruciton. Nicely done.

How the hell do you determine your bc when your bullet is wobbling out to 150 yards or so?!! I guess you just have to validate trajectory and play with short yardage bc in exbal and obviously your velocity? Wow... My head is starting to hurt.
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  #18  
Old 04-15-2008, 10:15 AM
Lightvarmint
 
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How does atmospheric conditions (temp, humidity, pressure, air density and density altitude) affect this phenomenon you guys are discussing? Additionally, how about range conditions (ie, mirage, wind and light levels)?

Reason I ask is that I had a very accurate precisely 6x284 tuned at sea level and actually won almost enough money with it to pay for one-half the gun.

Took the same gun and loading up to approximately a mile in altitude (ElPaso, TX) and the bullets would not stabilize at that altitude. I had to shoot a lighter bullet and also had to change to a slower burning powder all on the same gun to get the performance back to acceptable levels. When we left ElPaso and came back down in altitude, the old load worked just like before we went up in altitude.

I heard an interesting theory that the closer to sea level the quicker the bullets achieve stable flight conditions and therefore showed their short range grouping potential better at lower elevations than when fired at the higher elevations. If this holds true, then it would make it much easier to find the recipe for a gun to exhibit its true accuracy potential than having to conduct the same test at longer ranges where it is more difficult to account for accuracy affecting/robbing variables. The extreme would be conducting load testing at 100yards or 2000 yards. If the theory holds true, it would be easier and more accurate to take a 100 yard "bug-hole" load and test it at 2000 yards than to take the 2000 yard (.5 moa or 10") load and test it at 100. If the theory holds true, then the loading developed at 100 with minimal variables in conditions and then shot at 2000 would eclipse the accuracy potential of one developed at 2000 and then shot at 100.

For instance, this morning, we tested some bullets manufactured by Greyghostt (custom bullet maker for over 20 years) in Georgia and they were stable (here at 92ft above sea level) prior to 100 yards as evidence by the very small grouping (<.2"). We will test them again tomorrow for BC and longer range grouping ability by shooting over a chronograph (Oehler 35P) at longer distances to validate the 100 yard tests. These were aluminum tipped 338 bullets that should come in with a very high BC. These are .100" longer than greyghostts .265s we already tested at a BC of .770 at sea level (or calculated to a BC of > 1.0 at 10000 feet by another poster on this board) so these are fairly long bullets and should be very aerodynamically friendly.

Hopefully the 100 yard groups with the sleeping bullets were not a fluke. Anyway the bullets were grouping in a very predictable manner (ie, group geometry changing with seating depth changes).

James

Last edited by Lightvarmint; 04-15-2008 at 10:30 AM. Reason: clarification
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  #19  
Old 04-15-2008, 10:54 AM
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Quote:
Originally Posted by phorwath View Post
.

But I've come to learn that what they were probably saying all along (or perhaps I was misunderstanding all along) was that the moa calculated from the measured groups at longer distances was smaller than the moa calculated from the groupings measured at closer distances. light bulb

:confused: Or not. ;)


Exactly.............
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  #20  
Old 04-15-2008, 11:46 AM
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Lightvarmint,

That is an interesting theory. I'd be very curious to see what your results are tomorrow at longer range. Let me know what happens. I'm shooting in a higher altitude (which usually changes the station pressure) so I wonder if the lighter bullets will be easier to work with. I'm using H4831sc in a 7mm RM with the 168 vlds. I have been unable to shoot because my rifle is with my smith getting some work done.

Usually I'm at 6,000 ft plus when I shoot. If the 4831 doesn't work well maybe I'll go to the H1000 or Retumbo to see if the slower burning powder helps at all...and of course play with my seating depth. I think it's correct to assume that if you can get your bullet to stabalize at a shorter distance you're going to have better accuracy.
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  #21  
Old 04-15-2008, 03:11 PM
Lightvarmint
 
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Quote:
Originally Posted by drenge View Post
Lightvarmint,

That is an interesting theory. I'd be very curious to see what your results are tomorrow at longer range. Let me know what happens. I'm shooting in a higher altitude (which usually changes the station pressure) so I wonder if the lighter bullets will be easier to work with. I'm using H4831sc in a 7mm RM with the 168 vlds. I have been unable to shoot because my rifle is with my smith getting some work done.

Usually I'm at 6,000 ft plus when I shoot. If the 4831 doesn't work well maybe I'll go to the H1000 or Retumbo to see if the slower burning powder helps at all...and of course play with my seating depth. I think it's correct to assume that if you can get your bullet to stabalize at a shorter distance you're going to have better accuracy.
I would try the lighter ones before I canned the barrel.

The gun we are using has been tested and proven to be very accurate (using 300 smk bullets) on my private range that is fairly well shielded from the wind on all four sides. Guns are/were tested both at 100 and 900 yards with the same loads and the performance was almost a perfect cone of dispersion. And, we deployed wind flags to enable us to detect wind conditions. Oh, and we only shoot until about 9:00 a.m. to eliminate any affects due to ground mirage. Not as good as the Houston warehouse, but for longer distances, it is hard to beat. Almost forgot, we shoot at a target board that is 8 foot tall and has white stripes to use as an aiming point when shooting the drop charts. Normally, with the gun(s) zeroed at 400, the shots will fall on the target board within an inch of the vertical centerline.

Anyway, I think the theory points to the fact that if you can't tune the gun in conditions that have the absolute minimum of variables to allow the shooter squeeze out all that can be had, that the gun really isn't finely tuned at all unless by dumb luck or happenstance.

Years ago when they were shooting indoors at the "Houston Warehouse" it was like area 51. Accoriding to articles and reports on the shooting sessions, strange things occurred there and they shot with aritificial lighting at night and the skylights in the daytime. The owner of the warehouse (Virgil) could tune guns like a piano tuner and (according to written accounts and witnesses) he routinely shot in the .020-.050" range. The reason he could do this was that all the variables that one sees on the range were eliminated. Only the errors in load construction, components, guns/barrels and shooter ability could not be eliminated and they put on quite a show. Gunsmiths and shooters from all over the country would come to Houston and test their theories, loading techniques as well as case prep techniques to find out what worked and what did not work. If he took the gun outside and shot, it would obviously not perform as it had indoors, but it was tuned as good as it could be. BTW, some of the "secrets" he had about getting the consistent tiny groups were never revealed. He was a fanatic not just about neck thickness, but about neck tension. He would only shoot groups with cases that had the same number of firings to ensure the work hardening and the hardening due to shooting were as close as he could get them. He also found that different barrel lengths has different harmonic affects and that at a certain length provided the most consistent performance on target. He would take a barrel that started out long and systematically cut say .250 off and then recrown and shoot it until it satisfied him. I am sure that if he took the information he gleened from shooting in his shooters paradise and applied to to long range shooting, that he would really turn some heads and put on quite an impressive show.

Shooting inside is an priviledge that I do not have, but I learned long ago that by eliminating as many variables as possible usually results in better shot groupings. I have never seen a situation where removing variables resulted in worst perfomance on target.

Remember, the wind blows individual shots both into and out of groups.

Hopefully you will get your shooting stick back quickly so you can have some fun.

James
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