Spin and stability

When it comes to anything accuracy related, I'd take rpollock's opinion over just about anyone on this board. He knows he stuff and has been doing the business at the sharp end for a very long time. But hey, its the internet where everyone is an expert regardless of what they have actually done or accomplished.
 
coleman1495 said:
The effect of twist rate are on a per set-up basis. It will change depending on what bullet and set-up a person in using. There isn't anyway of knowing how changing twist rate will effect ballistics without testing it.
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The last sentence there is contradictory to Litz's published data on BC vs SG, which kombayoch linked to on the first page. That data indicates that as rpm increases, BC values asymptote to a constant. This is an important piece of information for equiptment decision making. By the trend in data, when shooting extended ranges, it appears better to have to much rpm than just enough. Conversely, on the short range, a slightly lower than ideal rpm may enhance accuracy by a measurable amount.

Why discuss the issue at all? Because over the years, components become scare from time to time, so ensuring versatility when chambering a new barrel may be wise. I will bet that topics such as these will become more and more common as the cost of access to the hobby skyrockets.
 
Incidentally, the emotional reactions along the thread here are neat to see- obviously this is a topic of interest. In one day it's gone much further than the typical 'what caliber should I buy' thread.
 
coleman1495 said:
Of course you can over spin a bullet. A particular rifle/set-up will react differently to the effects of twist rate.

There isn't any means of knowing what the effects of accuracy will be. A faster twist rate may shoot some bullets better than others. This will also change based on distance and MV. We know that spin effects BC and trajectory. It will effect this in a measurable way only for a particular set-up and load. There are too many variables to know exactly what will happen.

A person still has to test that particular set-up. No amount of theory will tell you what will happen. There is no amount of testing and calculations that a person could do at 100yds that is going to tell him what will happen at 800yds.

Try getting good accuracy from a light bullet out of a fast twist barrel. My experience has led me to find that it most certainly can have a detrimental effect on accuracy.
Click to expand...

Awesome... you get it.

Jerry
 
max-x said:
The last sentence there is contradictory to Litz's published data on BC vs SG, which kombayoch linked to on the first page. That data indicates that as rpm increases, BC values asymptote to a constant. This is an important piece of information for equiptment decision making. By the trend in data, when shooting extended ranges, it appears better to have to much rpm than just enough. Conversely, on the short range, a slightly lower than ideal rpm may enhance accuracy by a measurable amount.

Why discuss the issue at all? Because over the years, components become scare from time to time, so ensuring versatility when chambering a new barrel may be wise. I will bet that topics such as these will become more and more common as the cost of access to the hobby skyrockets.
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As I said before, this theory does not agree with all circumstances. It is far from complete. Test for yourself.

Yes, I have made the very large investment to test for myself... why I have complete confidence that things are not constant, even from lot to lot of bullets.

The current bullet tech is like balancing on a knife edge... if you test, you would see and understand. It would be great if current high BC bullets were as easy to set up as a Sierra 175gr MK... they are not.

Today, shooters are chambering for a bullet or at least bullet style. There will be a number of rifles at the Berger SW Nationals that will be built for 1 bullet only.

That can really narrow down the options on what works... so keep an eye on what the F'ers are doing. Might help.

Jerry
 
Jamie said:
I am just about ready to close this thread down.


Jerry seems to go the cheapest way guns barrels and so on so he preaches that ( and that's ok)

I don't know how he places in F class or TR or if he has ever shot PRS.

I do know Brain Litz knows his stuff and numbers. Better then any of us non rocket surgeons

I know Hornady and serria both make good bullets that are forgiving. Handle the jump of a factory rifle very well and group well

I know Lapua and Berger don't like a jump tend to not like factory chambers ( but some do shoot them)

I do know that if I put the right data in my AB program I get fantastic results ( 823 meter coyote kill with the first round)

I do know I have put 10 rounds threw one hole at 100 meters( pics and witnesses ) with Berger vld.

It just seems like there is a shat pile of back and forth going one and only one person is putting know data and research in here.
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I think you quite misunderstand... I go by tools that offer a tangible benefit over the alternatives. The fact that sometimes this stuff costs much less.... is a bonus to us all. I bet you are going to have a flip when the Rem 783 article comes out.

And sometimes, the best tool for a certain job is the most expensive.

You would be amazed at the level of training/education many top F'ers have. And the resources, some will put to improve their performance. Some times that investment highlights problems with current theories. This is not a bad thing... that is how the sport evolves.

When people stop looking for better answers, that's when things go sour.

Jerry
 
cdn shooter said:
Since the tone of the thread has prs shooters needing NASA worthy trajectory preparation I need to ask, what competion has unknown distances at ranges of 1700 and beyond? I can't seem to find one anywhere.
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No one said anything about unknown distances. Some matches may have stages with UKD, some may not. Often, you won't know till you get there.

Several CoF from past matches posted in this thread:
http://www.canadiangunnutz.com/forum/showthread.php/1306582-Prs-course-of-fire

Las Vegas match that happened in January had a stage out to 1760 (post #15). Distances and timings are listed (time includes all shots fired and any movement required).

There is an upcoming match posted right in our competition forum that is 500-1800:
http://www.canadiangunnutz.com/foru...d-Range-PRS-at-Q-Creek-Ranch-(500-1800-yards)

Go and shoot one. At any of these matches, first place will get a few thousand bucks cash or a custom rifle or both. People in the top 5 will walk away with cash and/or something like a high-end optic. More than enough to cover the entire cost of the trip (travel, food, rooms, ammo...).

Should be an easy win for any of these experts. They can even turn a nice profit after covering the cost of going. Will be a sure thing for them since PRS shooters obviously know nothing and are just shooting bulk FMJs at big steel targets.
 
No more arrogant than implying that we have no idea what we're doing and are shooting junk bullets. No more arrogant than calling people internet experts while also being a person on the internet endorsing another person on the internet who is slagging the work or a known expert with an array of respected publications.
 
Jerry, in your experience, say using a 10 twist 30 cal barrel but shooting a 155 gr bullet, is it an increase in group dispersion at distance that you see, or a divergence in come ups from expectation?
 
kombayotch said:
No more arrogant than implying that we have no idea what we're doing and are shooting junk bullets. No more arrogant than calling people internet experts while also being a person on the internet endorsing another person on the internet who is slagging the work or a known expert with an array of respected publications.
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I didn't slag anyone, I asked a question about prs. The slagging has been pretty one sided (prs superior to Fclass) which just isn't true. The same problems are clear in both styles. As Jerry pointed out F class sighters are not really sighters, a vbull is the expectation on the first round.

I don't know much about it because there just aren't any matches close by. There's one match a year in BC as far as I know. Just not enough to outfit an entire rifle for. And that match maxes out at 600m which doesn't take anymore planning than any other match.

Prs sounds fun, wish there were more matches around...hopefully it grows around here and I can get involved. But I don't plan to go back to school or to vegas to participate, will just practice and record my data for all ranges expected. Same as F class.
 
max-x said:
The last sentence there is contradictory to Litz's published data on BC vs SG, which kombayoch linked to on the first page. That data indicates that as rpm increases, BC values asymptote to a constant. This is an important piece of information for equiptment decision making. By the trend in data, when shooting extended ranges, it appears better to have to much rpm than just enough. Conversely, on the short range, a slightly lower than ideal rpm may enhance accuracy by a measurable amount.

Why discuss the issue at all? Because over the years, components become scare from time to time, so ensuring versatility when chambering a new barrel may be wise. I will bet that topics such as these will become more and more common as the cost of access to the hobby skyrockets.
Click to expand...

As you stated the data presented indicates that as rpm increases, BC values asymptote to a constant. You agree that this would change depending on the specific bullet used? Heck it you might even see substantial changes from lot to lot. Its excellent theory but you still need specific testing to determine what the constant would be for that particular bullet. The set-up might even change the constant.
 
kombayotch said:
No one said anything about unknown distances. Some matches may have stages with UKD, some may not. Often, you won't know till you get there.

Several CoF from past matches posted in this thread:
http://www.canadiangunnutz.com/forum/showthread.php/1306582-Prs-course-of-fire

Las Vegas match that happened in January had a stage out to 1760 (post #15). Distances and timings are listed (time includes all shots fired and any movement required).

There is an upcoming match posted right in our competition forum that is 500-1800:
http://www.canadiangunnutz.com/foru...d-Range-PRS-at-Q-Creek-Ranch-(500-1800-yards)

Go and shoot one. At any of these matches, first place will get a few thousand bucks cash or a custom rifle or both. People in the top 5 will walk away with cash and/or something like a high-end optic. More than enough to cover the entire cost of the trip (travel, food, rooms, ammo...).

Should be an easy win for any of these experts. They can even turn a nice profit after covering the cost of going. Will be a sure thing for them since PRS shooters obviously know nothing and are just shooting bulk FMJs at big steel targets.
Click to expand...

Yeah I really don't know much about long distance shooting.Feel free to school me if I am totally off the mark. I would imagine that winning a competition like that would require something along the lines of:
-purchase a suitable rifle/set-up
-Develop a suitable load. This will require a lot of R&D at your end. The load you developed may prove not to be sufficient. You may have to go back to the drawing board a few times.
-Test at a large variety of ranges. Again this will be a lot of R&D. The performance may not be sufficient.
-Observe the effect of wind on that particular set-up
-Practice, practice, and practice
-Be a good shot to begin with
-Get lucky

So in other words a person would have to do extensive testing, development, and practice in order to win an event like that. Where does the theory of spin and stability fall into that?
 
coleman1495 said:
Yeah I really don't know much about long distance shooting.Feel free to school me if I am totally off the mark. I would imagine that winning a competition like that would require something along the lines of:
-purchase a suitable rifle/set-up
-Develop a suitable load. This will require a lot of R&D at your end. The load you developed may prove not to be sufficient. You may have to go back to the drawing board a few times.
-Test at a large variety of ranges. Again this will be a lot of R&D. The performance may not be sufficient.
-Observe the effect of wind on that particular set-up
-Practice, practice, and practice
-Be a good shot to begin with
-Get lucky

So in other words a person would have to do extensive testing, development, and practice in order to win an event like that. Where does the theory of spin and stability fall into that?
Click to expand...

A little bit more than that to be successful in PRS.
-You're not just going to be shooting 90 degree to the target in some matches, so you're also going to need to learn how to adjust for shooting at upward and downward angles. Some stages are shooting at targets up on the side of a mountain, in some you are shooting from the mountain down at the target.
-How to read your wind without the use of flags down range, because there aren't any.
-How wind affects the bullet when shooting uphill or downhill.
-How to spot your own shots because you don't have a spotter or markers showing you where your misses are going.
-How to shoot at targets that are moving at different speeds and are at different distances.
-How to shoot moving and stationary targets from a moving position (ground vehicle or helicopter).
-How to range targets accurately under time limits.
-How to build a stable shooting position that isn't prone. You may shoot off of vehicles, out their windows, off of fences, tripods, rooftops, and a variety of other structures.
-How to shoot with your rifle laying on it's side (urban prone)
-How to shoot a target that you can't see (blocked by something half way between you and it), knowing that something directly above it is a certain height above it.
-How to shoot through a loophole (ex: 2"x2" hole in a wall that's 20 yards away) at targets that are hundreds of yards away without hitting the sides of the wall the hole is in.
-How to shoot standing, kneeling and off of your elbows. (vegetation may prevent a prone shot off the bipod).
-How to do all of these things shooting on your weak side (left handed if you're a righty or vice-versa)

Probably some other stuff I'm forgetting...

You never know what the stage will look like until you get there, just as you will never know where your target will be in real life and how you will be able to support the rifle if you go out hunting or whatever. That's the point of it; to be able to adapt to whatever the situation is and still make a shot on the target in a timely manner. How are you going to test for all of these thing? For every possible variation of them? You can't! You need to rely on ballistics calculators whether you're doing the calculations there or ahead of time and making charts. You need to gather as much data as you can to calibrate it, but you'll never be able to test every scenario.

All of the trajectory related things above can be figured out with a ballistics calculator like JBM. But you need good data to put into it. You need good velocity, a good BC number, accurate scope height, accurate environmental data, velocity change with temperature data. The more you can minimize the number of variables or the amount they change, the better off you will be. Things like choosing a temperature stable powder or a barrel twist that stabilizes your bullet enough to keep the BC from changing when the temperature does (SG > 1.5) will help you.
 
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Okay so provided you have everything that you listed:
-good velocity, a good BC number, accurate scope height, accurate environmental data, velocity change with temperature data.

Provided your rifle is zeroed to start, could you use your ballistics calculator to determine what adjustments to make at a reasonably far distance? Lets say 800yds? This would be assuming you haven't already tested it.
 
max-x said:
Jerry, in your experience, say using a 10 twist 30 cal barrel but shooting a 155 gr bullet, is it an increase in group dispersion at distance that you see, or a divergence in come ups from expectation?
Click to expand...

I have shot the 155gr Amax and it was great in a 12 twist out to 1450yds. Throat lengths currently on my barrels are WAY too long to be of any good for the 155gr family.

We know that TR shooters don't go over 12 twist with most using 13 twist.... you can see what SG they have chosen to use and they had what, 70yrs to test??? and there are TR shooters in many commonwealth country including the USA so just a few shooters collecting data.

Remember, that light for caliber bullets are FAR LESS sensitive to spin RPM's then super heavy slugs for calibre. Why 50gr 22cal bullets can be zapped out of 22-250's at extreme RPMs and velocities without making a fuss.

Try that with a 90gr VLD and I bet more care has to be made with twist rates (yes, I have shot this combo)

Also, many current heavy for calibre bullet planforms have been "distorted" from past form factors to try and produce a very high BC value. These shapes can have some serious quirks that vary with velocity, twist, bore condition, ambient AND distance/impact velocity.

The current models do not describe what we see on target... again, not saying the models are bad... just they are not complete. Right or wrong, I get scored by the holes in the target not the books I bring to the match.

Several popular bullets have been redesigned... I shoot one of these and have had to redo all my load tuning AND barrel twist. I sure hope the new design is even better then it was... DAMN SNOW.

Will more designs get tweaked? I fully expect that.. but a whole lot of shooting OUTSIDE the bullet companies is going to get done first. When competitors start reporting and/or complaining, then slowly things get tweaked.

Yes, bullet manfs do some testing of every bullet they offer BUT I question how thorough or aggressive they test????

I love how far and fast bullet tech has come in the last 5 yrs BUT with any rapid advance, there are collateral problems that aren't/weren't accounted for.

Believe me when I say I would be far happier to just load my bullet X over so many grains of powder Y, 15 thou off the lands in a standard twist barrel and send it... and do all my testing at 250yds (local range). I have had to push my testing beyond 800m cause that wasn't good enough... Joy!

For older traditional designs, the models can work but many aren't using these because of a number.

Two lots... two quite different set ups... Is this an isolated case???

So can I give anyone an answer to all the possible outcomes with current new gen bullets? Nope, except to make competitors and LR enthusiasts aware to keep vigilante on their testing and results. Don't discount when things dont make any sense.

It may very well be the bullet and how it interacts with the barrel twist...

YMMV.

Jerry
 
k, can you explain where ambient temp can affect BC?

It most certainly affects the air the bullet flies through but affects ALL bullets regardless of size, shape or BC. I am not seeing how temp can affect RPM decay to any meaningful degree.

I have seen some dramatic changes in elevation due to changes in Sunlight - and that change happens NOW.

But even with a 30C range of temp, the zero seems to be solid at 1000yds... Certainly, changes that are way smaller then you would notice in PRS style of shooting.

I pay attention to cloud cover WAY more then temp and I am sure you can imagine I shoot in some pretty wide temp ranges.

Could changes in temp be affecting other aspects of the ammo and rifle and shooter that may be affecting the results at distance?
Jerry
 
coleman1495 said:
Okay so provided you have everything that you listed:
-good velocity, a good BC number, accurate scope height, accurate environmental data, velocity change with temperature data.

Provided your rifle is zeroed to start, could you use your ballistics calculator to determine what adjustments to make at a reasonably far distance? Lets say 800yds? This would be assuming you haven't already tested it.
Click to expand...

You need to test out as far as you can to calibrate the ballistics calculator. But, think about what you're doing when you go and shoot at a longer distance to calibrate the calculator. You're not going to trial and error it all the way out. You plug the numbers you have to get an adjustment and then fire at different distances, adjust as necessary at each one, then true the calculator based on the results. Every time I have done this, I have been able to get onto a reasonable size target at whatever distance with the original ballistics calculator output. When I shot the Grind in the fall, I was only able to test out to 700 yards before leaving for the match. On the tune-up day we were able to fire out to 1200 yards and the calculator's output (with my 700 yard calibration) was only 0.1 mil low.

Not every match has a practice day where you can shoot more than a 100 yards zero. You sometimes have to rely on the ballistics calculator, and you may be shooting at a location that has a much different air density than where you calibrate and practice. They same people's name keep appearing at the top in matches, and these people are shooting all over the US in places that have very different air densities. Everyone is using Kestrels and some have expensive ballistics software like Field Firing Solutions that can figure out many of the things above. That they keep winning implies that they can and do rely on the ballistic calculator's data.
 
After looking up Bench rest shooting I don't think it's a sport I could stay in it long. While the groups sizes are scary small ( and I appreciate the hard work and time to get it) it's to much like trap and skeet. The same COF everytime you shoot.


That is why 3 gun and IPSC are the matches I can't get enough of! Solving problems on a different COF every time!


So I guess the point of this is BR bullets will not work well for us. And our VLD's won't work the best for BR

Jerry it was not a Dig at you I just remember all the lower end project guns you have worked with over the years
 
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