Spin and stability

I have been following this thread with interest. Guys on this board talk about shooting 700 yards or 1700 yards. I am lucky to have an approved 500 meter range with concrete benches 20 minutes from my house. Looking through my notes, how many guys on this board have measured a box of 500 Sierra bullets base to ogive with a comparator to find a difference of .0085" and they appear to have been made in 2 different dies? How does that effect the SG, BC and your vertical at 700 or 1700 yards? We are talking real world trying to get bullets to land at least close to each other on paper regardless of range.

How many guys on this board made the investment in time and equipment to make their own custom hand swaged bullets because they can make a better bullet than the commercial bullets you can buy? How many guys on this board experiment with the shape of their homemade bullets and test them in a rail gun? There's for sure 2, and possibly 3 guys on this board that make and test their own bullets and compete at the highest level internationally and when they talk bullets and twist, I tend to have faith in what they have to say.
 
As you point out; only 2 or 3 people on the entire board are set up to make their own custom hand swaged bullets. Few have the money to buy the equipment and experiment with that or the time to do it. If they do, there is a forum for that below where you can discuss homemade bullets till your hearts content. Most serious about long range will buy bullets from a manufacturer like Berger or Lapua (most popular in both F-Class and PRS) and sort them in whatever way if they don't feel their quality is up to par out of the box. That isn't going to change.

There is no doubt in anyones mind that a higher quality, more consistent bullet is going to produce more consistent results. That's common sense. No one is arguing that. So why you guys keep bringing it up is beyond me. Sort your bullets for better consistentcy or make your own if you have the time, money and inclination to do so. Agreed, let's move on.

Edit: for the record, I have a swaging press, the ability to make my own dies:
http://www.canadiangunnutz.com/forum/showthread.php/634348-Homemade-swaging-press

What I don't have: time to play with that stuff.
 
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I have to admit, it has been a real struggle to read through this thread. It has been even more of a struggle to find some information which would add to my admittedly pitiful store of knowledge and perhaps, help me in competition going forward. Boiled down to the basics, I have learned that everyone wants good bullets (duh!). I have also learned that F-Class shoters have amassed a great deal of experience and considerable data regarding ballistic consistency but that this body of knowledge is suspect at best because they have convertible sighters and know how far they are shooting. This also shows why they can hardly be considered to be real men like the tactical guys are. I have learned that Harold Vaughn was either a messiah or a fraud and that Briam Litz falls into the same category dependent upon your point of view.
Because I don't spend a lot of time poring over virtual findings and in fact, almost try to avoid having my thought process contaminated, I am just a little old-fashioned in the way I do things and am occasionally a bit of a contrarian.
I have always maintained that BC is inconsequential, within reason, but that consistency was everything. I also felt this consistency was best measured by the results on the target. I don't give a rat's hindquarters what someone's computer modeling reveals. My concern is what happens on the range. If I get good results, with a given combination, then it is a good combination regardless what the interweb tells me. I live and shoot in the real world and that is what I am concerned with. For longrange shooting, I firmly believe one is best served by having sufficient twist. At short range, I actually feel the same way and if choosing between a fourteen and a fiftenn, will go with the quicker twist just on priciple. Maybe not the most cerebral method but I'm OK with it. By the way, when I compete I use sighters and I'm sorry if that makes me a bad person.
 
Bryan has done wonderful things for our shooting sports, Berger would not be what they are today if not for him, and I have the utmost respect for his
work.
However, in all fairness he is not the only ballistician in the game and as scientists go there would be debates I'm pretty sure.

I remember McCoys view on this would have been over spinning would result in shedding energy quicker? I am by no means suggesting that to be true, just saying.
Now then, why do we keep going full circle on this?? A few years ago everyone was twisting as tight as possible only to find bullets were blowing up. It doesn't matter
whos bullet it was, it all falls back on not only the thickness but also the malleability of a particular lot of jackets.

There is a point of diminishing returns on everything, would you rather have an accurate load and drop a point because you missed a switch or drop 5 or 10 because
your bullet didn't make it to the target? For me I'm quite happy with option 1.
 
kombayotch said:
SG is temperature dependent.
Click to expand...

If SG is affected by temp and SG is an indicator of BC "consistency", then I am not seeing it on target at 1000yds.

I see a direct correlation to temp... absolutely, but that can be easily explained by altitude/density calcs... ie hot air is less dense then cool air so you experience less drag/drop. Dry air vs wet air and so forth

If temp does affect bullet drag, then we should see some change in elevation in varying temps. The change, if any is simply too small for most of us to worry about or discuss. I just can't see it being a serious negative in PRS.

Where I think a real problem lies in changes in ambient light. With some mirage conditions, this can cause a 1/2 to 1 min change in impact elevation and it does it fast... on or off. Shoot under a patchy cloudy day and it can give you whiplash trying to keep up.

The worst is that big cloud pushing a shadow over the range... Trainwreck coming since there is both the effect of light AND weather.

Given the type of desert like terrain I see many PRS matches shot on, localised temp changes can cause all sorts of micro density changes... we certainly get hammered by these on large ranges like Raton and Phoenix so I know it is very real.

Then there are thermals which in some parts can be massive and move at crazy velocities. On hilly ranges, you have drafts that can move at various altitudes and in varying directions. You can see the variations in some of the videos of PRS matches.. mirage and flags don't agree.

I am not saying the physical drag of the bullet may not be affected, I am just saying there are so many environmental effects that are so much bigger in net result.

No wind flags, not enough time to stare at the conditions, what are PRS competitors NOT seeing. Not very comforting when you are on the clock to get shots on target and the only aid is an LCD screen. If you can, I would pack a set of low mag binos and start glassing

I dont see alot of PRS shooters glassing in these videos. Compare that to an F class match.

As I get more time, I would be happy to put some current 6mm and 6.5 bullets down range out as far as you think you will compete and see how they track vs the ballistics program. I got the real estate to test so not a problem to see what changes over time and weather.

I know the power that F class offers other forms of LR competition is a very stable test bed for info. The only thing we care about, or hope to care about is the air. We don't have to worry about elevated heart beats, wobbly shooting locations or awkward target presentations.

If BC is affected by ambient temp, we simply aren't seeing it... or it is buried in other more important ambient changes.

When shooting PRS, I would focus on other environmental conditions and trust that my bullet is flying as it should... or at least have proven the bullet is flying as it should.

Worrying about a possible 2% change in drag pales in comparison to a change in ambient that can amount to minutes of change.

Jerry
 
Jerry, I think that your observations there are spot on. The high school-ish banter of which discipline actually knows which end of the rifle is supposed to be pointed downrange blissfully ignores both the dependency and cooperation the various disciplines are subject to for progress (and survival).

The only skepticism I have on the temperature dependent front is that at the density altitudes that are present both in the valley and in Arizona, the low end SG compromises do not show up. This is the surprise that caught David Tubb years ago when he rolled into the deep south to shoot a match and found that he wasn't in 'Kansas' anymore... This issue is one which we in the east are more often exposed to.
 
For clarity, the issue in question mentioned above is that of when the ambient density altitude is such that despite using a 'stable' powder, your Vo drops such that your SG decreases an amount enough to affect BC, or, as discussed previously, show negative effects in epicyclic swerve.
 
Bill Leeper thanks for your post. I agree with you.

I could care less about anything in my game other than what the bullets are showing me on paper.

That is why we do not preload. We load after every target and what we believe the target is telling us the rifle wants.
 
max-x said:
Jerry, I think that your observations there are spot on. The high school-ish banter of which discipline actually knows which end of the rifle is supposed to be pointed downrange blissfully ignores both the dependency and cooperation the various disciplines are subject to for progress (and survival).

The only skepticism I have on the temperature dependent front is that at the density altitudes that are present both in the valley and in Arizona, the low end SG compromises do not show up. This is the surprise that caught David Tubb years ago when he rolled into the deep south to shoot a match and found that he wasn't in 'Kansas' anymore... This issue is one which we in the east are more often exposed to.
Click to expand...

And this is why you have to test or at least be aware of possible changes. New gen bullets are not tolerant of a wide range of variation... they like what they like and it is best to figure out what twist vs velocity is best for THAT bullet. I have never said that a certain RPM is good or bad... it is a case by case basis and there are some real big surprises out there.

In the perfect world, you would test where you compete. Not always possible but then you better test in as similar a condition as possible. Some bullets may need very high twist rates, others far less.

The math doesn't cover it anymore. And I have yet to see anything account for changes as you go transonic.

Sure have had my share of WTF moments

Jerry
 
The part I don't buy is that the math doesn't cover it 'anymore'. When did math go from being descriptive and reflective to becoming obsolete. The fundamental purpose of math (beyond accountancy) is that it describes motion. Sometime over the last 30 years, higher level math devolved from a productivity tool to voodoo. Soon after, otherwise reasonable folks began discounting the knowledge and methods which proved thousands of tons of steel could float in water, that a rocket could sling a capsule to the moon and back, and that a big plastic tube could transport 400 people from New York to Paris in ten hours and not touch the ground between those two places.

To say that these new bullets defy all methods of physical description (ie physics) promotes head scratching.

Transonic is difficult to model due to the random nature of flow seperation, but that separation event only occurs as the trailing shock dissipates, and is not present before or after. Therefore, an otherwise very accurate model should be possible with a defined area of uncertainty at the transonic region, which I would suspect only extends over a 50 yard distance or less. It has also been empirically proven that boat tail design can mitigate the effects of this event.
 
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Oh I am sure someday, things will get sorted out but that is not where we are with some bullets today.

As I said, the math is not complete and there is stuff going on that is not predicted by what we know.... or at least what we think we know.

But then it wasn't until recently did we use G7 values vs the industry standard G1

Wasn't recently that doppler radar apparently picked up melting plastic tips.

Math has never stood still and continues to be modified to fit and answer more questions of what we know of our world.

The stuff we are trying to explain needs math that is well beyond the smartphone programs. Maybe it has more to do with dynamic stability and bullet design? Not going to argue that point as I have no idea where to look.

But shoot bullets way out there. Track where they should go and where they end up. Why they change and why they don't. Test various parameters and see if you can get things to work out. Maybe your math skills can help us understand what is going on.

Speeds where weird stuff can happen starts as early as 1700fps which is way faster then what we call transonic. Is it all in the head? who knows but there are more and more shooters seeing the same weirdness.

And maybe it will get resolved with versions 2.0 or 3.0? I know I am using 2.0 in my bullet of choice.

Jerry
 
If so many things affect BC #'s, seems manufacturers should start listing what conditions their #'s were achieved under(fps, twist rate, atmospheric, moon alignment) eh?

Would be nice to see a few other manufacturers compete with Berger in F-class with special high BC bullets, but maybe its too small a market to bother.
 
Sierra lists the BC change vs velocity... they shoot in a tunnel so likely it is a controlled ambient????

why they list their data using G1 curves, I have no idea but that is a pretty clear case where old styles keep on going.... and does that lead to bad inputs to ballistic programs?

The variables are several... to create any type of broad range data would be a massive undertaking. Given how very few shooters will actually be able to utilise this info to its fullest, close enough is good enough. We worry about BC's in the 2nd decimal place, alot of scopes don't have consistent click values so....

Wasn't too long ago, all the BC numbers were just a computational estimate spit out by the program that designed the bullets.

Things are moving forward and getting more accurate BUT there is still a long ways to go AND alot of debugging to happen with new gen bullet shapes.

Jerry
 
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