Spin and stability

Consistency trumps all else in F-Class (so the people who win at it tell me). If changing your BC changes your first shot POI by several inches, no big deal. Correct off the sighting markers and carry on. You're usually shooting shorter distances before going to the longer ones, which also lessens the impact. For us that's a zero for that shot... And you'll probably have 40 or more first shots in a match since you're generally only taking 2 at each target. And the first shot is often worth more than the second shot. Plus your relay may also shoot an ultra long stage as their first stage.

Consider that the difference between a 0.4 MOA load and a 0.3 MOA load is 0.74" difference in radius at 1400 yards. A 6% reduction is BC is around a 53" change in drop. The ratio stays basically the same at different distances. 6% reduction is what you're going to have shooting a 105 Hybrid out of a 1-8 twist in spring temperatures... It's pretty easy to see what to focus on.
 
kombayotch said:
Thank you, I'm glad you find it useful.

Magazines like Precision Shooting had some good info go through them. Unfortunately, there isn't much in the way of data from matches stateside. It wasn't until around 2000 when matches started to adopt a practical format. Traditionally, matches were on square ranges at known distances. They always had big target boards and shots were marked with markers to show where the shots were going. Since sighter shots were given, many things could be ignored. Weapon systems weren't as accurate and there were no handheld computers to process ballistic models. We have come a long way because of people like Bryan. Unfortunately, we don't appreciate it as much up here because most of our matches haven't been modernized like they have in the US.
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This is spot on!
 
Jerry, your advice here is quite confusing- each of your posts have a segment somewhere that says 'no one knows how or why things behave the way they do, so whatever you convince yourself of is correct and go make some noise to confirm or disprove it'. While this mantra might suffice for government work, discounting basic physics so consistently is poor marketing. One of the motivating factors in this analysis is to gain knowledge in proper barrel selection in preparation for competition. Putting some traces of your data out there to support the hand waving would be quite helpful for folks who may be thinking of buying a barrel from you. The alternative response of 'buy three different twists and amaze yourself' turns suspect (don't forget a barrel usually lasts 2k rounds 'on average', and hence, costs approx $0.40 per shot!). We know that you can hook us up with a barrel- folks need to understand which barrel they are looking for to begin with.

Do you have any concrete data to share? What quirks have you seen in your years of ranges past 800m and SGS under 1.5?
 
Testing with my 308 now covers 4 twist rates and a whole lot of other specs. 8 barrels and counting

I am about to add another twist this year. Yeah, I am all too familiar with SG.

The bullets I competed with in Montana last Sept is not the same bullet I have sitting on my bench now... same name, different lot, very different bullet. I doubt this will be an isolated case.

I am redoing my testing... JOY. What worked before is not working now... The SG wouldn't have changed but the results sure have.

So, you can take it for what it is. Either I have alot of testing and a alot of info... or one of the worst developers of LR precision.

You are asking for 1 defined answer... I would LOVE that too. I can tell you that the fence posts keep moving so you better be prepared to test in anticipation that change can and will occur.

And the rate at which bullet manfs are changing the bullet shapes, this is going to be a very fun couple of years.

To add to the confusion, if going way out there, better start testing supersonic and transonic and even subsonic performance. Changing bullet shape to appeal to one parameter can and will have affects on others.

Sorry, there is not one simple answer....not anymore.

Jerry
 
This will be one of the rare times I agree with Jerry! There is way more going on with bullets than just looking at BC, twist, and external form of the bullets. It may surprise a lot of folks to find that in the short range BR world, that we shoot mostly bullets around 1.00 stability factor, sometimes a bit more sometimes even less than 1.00 even though the models say it isn't possible. Never much over 1.2 as high BC bullets don't perform well at short ranges. Just the way it is. Lots have tried.

Now if I told you that a good flat base bullet with a lousy BC, can outperform a boat tail with a higher BC at shorter ranges in terms of drift, then there would be a rioting in the streets and everyone says you don't know what you are talking about. See it for yourself some day. We see it in BR all the time, but current mathematical models don't account for it. That is why nobody in our group actually cares about what the models predict. Only thing that matters is the paper.

If I said some guys have a 100 yard bullet and a different bullet for 200 yards, or even a windy day bullet vs a calm day bullet then what? Probably all made in the same point up die as well! These types of subtle gains don't show up in any models, but they are there. These guys are the best in the world so hard to argue with what works for them.

It is important to separate the commercial world from the competition world. In our game almost everyone does their own swaging of bullets, or has a fellow competitor do it for them. It is a lousy task, worse than precision reloading for a time consumer, but you do it anyway. You have to, to run at the front. I predict f-class won't be far behind.
 
It's important to separate the square range competition world from the practical field-oriented competition world. The former ignores the first shots fired at each distance. For the latter, the first shot out of your barrel in the morning and the first shot at every distance/target can make up 66% of your score (3 pts. for a cold bore hit then 2 pts. for a 1st round hit, 1 pt. for a 2nd round hit on each target, which are all at odd random distances). The things that allow you to predict where that bullet is going to go trumps small gains in group size for the latter.

Even if you test your load out to extreme distances and calibrate with that data, your BC will change when temperature changes if you haven't chosen your twist for the lowest temperature you will be shooting in. SG drops as temperature drops, and rises when temperature rises. That means that in addition to having to deal with the change in trajectory due to air density change and velocity change of the powder with temperature, you now have a BC that's also changing. There isn't anything you can do about the change in air density, but you can pick more temperature stable powders and barrels that have sufficient twist to stop the BC from being compromised to mitigate those two factors.
 
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From a PRS perspective, ballistic tables and solutions are paramount as previously mentioned. At random target distances first round hits are crucial. This depends on the math; it needs to be correct.

Bryan Litz began his career developing air to air ballistic missile technology. The US government paid him to design accellerating projectiles travelling at mach 4+ to hit other moving targets at similar speed. His knowledge base and interest in long range precision shooting has been eye-opening for many people in this industry. When someone like Bryan Litz who is highly educated comes from a data- driven aerospace industry it forces everyone to think outside the box and and accept new ideas. For example, some people may be aware of Harold Vaughn who also came from an aerospace background; he published a book on rifle accuracy years ago. It was data driven, not based on opinion and it was a huge contribution to the people who were willing to accept new ideas and philosophy.

If Bryan Litz says to use a faster twist for a given bullet at X temperature and Y speed, I accept his solutions as likely correct. What have we got to loose by ordering our next barrel with a 1/7.5 versus 1/8 twist? He does not have a history of being wrong!

If we can predict the solutions to variables that we can control we would be foolish to not take every opportunity to reduce our lack of repeatability.
 
Each competitor in each discipline faces the same set of challenges and restrictions as his fellow competitor, be it cold bore shots or whatever the task at hand is. This doesn't make any one discipline special ballistically, at the top they are all incredibly difficult and require the best possible equipment solutions.

The point is there is lot more to bullet performance, even at very long range, than reading the BC on the side of the box or matching barrel twist to OEM recommendations. All I am saying is keep an open mind to other influences on how the bullet goes down range. Is the jacket any good? Is the core any good? What effect does displacing the jacket and core on a long boat tail have? Does it point up evenly in the point up die? Are the swaging dies wore out? Did the bullets bounce around a UPS truck or get dropped and get damaged? In an effort to maximize BC does the designer/manufacturer give up performance somewhere else? What shortcuts is the manufacturer taking to maximize their return on investment? Think about the nice shiny bullets when you first open the box, how long did they tumble them just to make them look shiny, does that degrade performance just to look nice?

Or you go with the highest possible BC bullet you can buy.
 
Insite Arms said:
For example, some people may be aware of Harold Vaughn who also came from an aerospace background; he published a book on rifle accuracy years ago. It was data driven, not based on opinion and it was a huge contribution to the people who were willing to accept new ideas and philosophy.
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Harold Vaughn has also been widely discredited, for many reasons, one of which was using a 270 winchester and hunting bullets to do the bulk of his testing and research. The vast majority of his results could be labelled as research noise.
 
From a practical perspective, IMO using a fast twist rate is detrimental to shorter range accuracy. As you get out farther and the bullet slows down a faster twist rate is beneficial. I have seen some freaky bad accuracy from firing light cheap bullets out of a fast barrel.It seems like faster twist rates are popular. I know when I rebarreled my rifle the seller of the barrel was one of the few people who didn't want to sell me a faster twist.


Now how it affects BC and wind stability. I dunno. I would imagine folks like Bryan Litz probably have a pretty good idea of what happens. I did a few various labs in college where we tried to prove a known fact (like the molar mass of gasses or Avogadros Number). It was all done for educational purpose. Proving something to both show the technique and the theory.

It was pretty rare that a lab worked out so it illustrated things that were accepted as facts. There is simply too many variables in the real world to be able to know what will happen. What works in one situation may not work in the next. Actual development and testing will still reign supreme.
 
rpollock said:
Each competitor in each discipline faces the same set of challenges and restrictions as his fellow competitor, be it cold bore shots or whatever the task at hand is. This doesn't make any one discipline special ballistically, at the top they are all incredibly difficult and require the best possible equipment solutions.

The point is there is lot more to bullet performance, even at very long range, than reading the BC on the side of the box or matching barrel twist to OEM recommendations. All I am saying is keep an open mind to other influences on how the bullet goes down range. Is the jacket any good? Is the core any good? What effect does displacing the jacket and core on a long boat tail have? Does it point up evenly in the point up die? Are the swaging dies wore out? Did the bullets bounce around a UPS truck or get dropped and get damaged? In an effort to maximize BC does the designer/manufacturer give up performance somewhere else? What shortcuts is the manufacturer taking to maximize their return on investment? Think about the nice shiny bullets when you first open the box, how long did they tumble them just to make them look shiny, does that degrade performance just to look nice?

Or you go with the highest possible BC bullet you can buy.
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If you're understanding is that our concern is about having the highest BC, then you really aren't getting it. For us, it's not about having the highest BC, it's about having a consistent BC. Not in the same way as the F-Class shooters want it to be consistent though. They want each bullet to be identical, but for them it doesn't matter if it changes with temperature as long as all of them change the same. Their sighter shots will negate the change. The change can kill us. We don't want the BC changing when temperature changes. For us, the next shooting season starts the day after the previous one has ended. There is no winter break. We want the BC to be the same when it's it 40F as when its 100F.
 
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coleman1495 said:
It was pretty rare that a lab worked out so it illustrated things that were accepted as facts. There is simply too many variables in the real world to be able to know what will happen. What works in one situation may not work in the next. Actual development and testing will still reign supreme.
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Men have landed on the moon and rovers have been put on Mars without going through a trial-and-error process for the landing. Most electronic circuits are built based on models and theory.

The thing with models and calculations is that if you put garbage into them, you get garbage out. Sloppy college experiments, performed by students with poor lab skills does not set the standard for the accuracy of models by a long shot. Those same experiments, when performed by skilled and competent lab personnel, do match up extremely well to the real world results.
 
kombayotch said:
If you're understanding is that our concern is about having the highest BC, then you really aren't getting it. For us, it's not about having the highest BC, it's about having a consistent BC. It's about the BC not changing on you when temperature changes. And for us, the next shooting season starts the day after the previous one has ended. There is no winter break.
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That's weird. You argued for higher BC a few posts back.
 
kombayotch said:
Practical shooters wants higher BC for good reason. Reducing BC a little may not matter when you're shooting at a canned 1000y/900m with a big magnum, sighters and marked shots, but it does matter when you're shooting out to a mile with a small 6mm and all of your shots count.
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Found it.
 
How about we put the whole quote so that the first sentence is put into context.

kombayotch said:
Practical shooters wants higher BC for good reason. Reducing BC a little may not matter when you're shooting at a canned 1000y/900m with a big magnum, sighters and marked shots, but it does matter when you're shooting out to a mile with a small 6mm and all of your shots count. Having an accurate BC matters a lot to those who don't have the facility to test out as far as some of these matches are shooting, to true their ballistics calculators. They have to rely on the published numbers being accurate enough to at least get them close enough to correct the miss (and there isn't an 8 foot target board and markers showing that miss). An accurate firing solution will get you more points in PRS than a slightly smaller group. I'm only able to test out to 700 yards, so I have to rely on my BC being accurate when I shoot at further distances. So far it has been, but I've been diligent in making sure that my barrel and load combination are not compromising it. I don't need a compromised BC on top of the variation already there from manufacturing tolerances and having to deal with velocity changes from temperature.
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Yes, we want a high BC due to the distances (it's required - your short range BR bullets won't cut it, sorry), but the point of the post was that there are no sighters and the BC is being relied upon for an accurate firing solution.

Even in the first sentence, I was talking about BC changing, not the BC being lower due to bullet design.
 
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kombayotch said:
How about we put the whole quote so that the first sentence is put into context.



Yes, we want a high BC due to the distances (it's required - your short range BR bullets won't cut it, sorry), but the point of the post was that there are no sighters and the BC is being relied upon for an accurate firing solution.
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We get that you don't have sighters. I suppose no one does in PRS so you are all on equal footing. Seems fair to the people interested in this discipline.

Then you reiterate you do want a high BC. Nothing has changed. Still way more to a good bullet than only BC or consistent BC as you say. You can't get around that. Just one of many challenges facing shooters of all disciplines, hardly unique to PRS.
 
You're focused on bullet design when the issue we are talking about will happen with EVERY bullet design if the bullet is not fully stabilized. Regardless of what bullet design you have or how good it is, if you're BC changes on you because the bullet isn't fully stabilized, your firing solution will not be accurate unless you also account for that. Why add another variable to the mix when you don't need to? Smart shooters don't. They just pick a barrel twist that eliminates that variable.
 
I would love too see the F class guys try PRS. I bet most would not come back when the scores come out.

That's why I have problems with the shotgun sports. The same course of fire every time.

I shoot 3 gun. IPSC and IDPA.I also hunt semi long ranges 100/500 for deer and 100-800 on wolves. I see PRS my next focus. Even if I have to build a COF with friends at our 1600 meter spot.
 
You guys are on the top of the heap, no question about that.Laugh2 I can definitely see that PRS is a very disciplined sport though. There is a few f-ers that do play PRS
Dont quite understand why the chip?

Jamie said:
I would love too see the F class guys try PRS. I bet most would not come back when the scores come out.

That's why I have problems with the shotgun sports. The same course of fire every time.

I shoot 3 gun. IPSC and IDPA.I also hunt semi long ranges 100/500 for deer and 100-800 on wolves. I see PRS my next focus. Even if I have to build a COF with friends at our 1600 meter spot.
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kombayotch said:
You're focused on bullet design when the issue we are talking about will happen with EVERY bullet design if the bullet is not fully stabilized. Regardless of what bullet design you have or how good it is, if you're BC changes on you because the bullet isn't fully stabilized, your firing solution will not be accurate unless you also account for that. Why add another variable to the mix when you don't need to? Smart shooters don't. They just pick a barrel twist that eliminates that variable.
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Now we are getting somewhere. This is what I am getting at. Stabilization issues leading to loss of BC can be magnified by the bullet itself irregardless of twist or temp. Not every bullet is created equal, not even in the same box. Stabilization and observed BC is a lot more than just picking the right twist for the temp you intend to deploy it at. If you want perfect BC shot to shot you are hamstrung by the bullet manufacturing process itself. It is prone to a lot of issues. This is why people often refer to a particular "lot#" when looking for a good bullet for seemingly identical bullets. Or why there was a migration away from mass produced bullets decades ago in the BR world. Just saying to keep an open mind, and all is not as it seems in the bullet biz. The more you dig into this you will find a lot of unanswered questions about the bullet itself that have nothing to do with shape, published BC's, barrel twist, air temperature etc.
 
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