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Post by Kyle on Apr 1, 2016 12:20:57 GMT -5
Does a bullet's BC always hold true for drop and drift? Who has noticed examples where it does not? Do you have a explanation or educated guess as to why it does not if that is the case?
Edit. To clarify my question: Has anyone noticed where a BC was spot on for a bullet in terms of drop but not spot on in a known, measured wind condition?
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Post by bestill458 on Apr 1, 2016 12:28:19 GMT -5
Temperature, altitude, humidity and velocity would change b.c. imo!
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Post by Kyle on Apr 1, 2016 13:16:24 GMT -5
Temperature, altitude, humidity and velocity would change b.c. imo! All of these absolutely will. To clarify my question: Has anyone noticed where a BC was spot on for a Bullet in terms of drop but not spot on in a known, measured wind condition? |
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Post by elkman1310 on Apr 1, 2016 14:05:37 GMT -5
Kyle wind is a condition you can only read at the locating your shooting from the longer the distance the more variable come into play. I have shot groups at one mile and beyond at different elevations. The B.C. if its not over stated usually is very close even at extreme distances. The wind is never constant over 1,000 or 2,000 yards. So I really don't concern myself with wind drift on a chart. I have had 30 MOA of wind drift at 2,000 yards and also have shot at the same distance with zero windage even though the wind was not calm where we shot from.
There is a spin drift calculation that comes into play at long ranges but since were talking about 500 or 600 yards and we use a 1-18 or 1-22 twist barrel the slower the twist the less spin drift is calculated. I have shot extreme ranges for the last 30 years. With special long range guns not muzzleloaders. Our muzzleloaders still fall into short to medium range at best.
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Post by keith on Apr 1, 2016 14:41:45 GMT -5
This is one of my all time favorite myths. I'm not sure where it started but it is misinformation. If your drop and drift BC appear to be different it is because you did not accurately assess your wind speed and direction. The other possibility (not for BC discrepancy, just your impression of BC discrepancy) is that you do not know if your scope adjusts accurately because you never tested it.
The most important piece of info when trying to make any meaningful analysis of bullet flight is having an accurate BC. That value is a measure of how well a bullet penetrates air so it is easy to understand why it is important; that is what a bullet does since we don't shoot in a vacuum. To my knowledge, NONE of the bullets used in our SML's have been tested to a high degree of accuracy. Some were calculated and some were tested to the limits of what was available but they are not spot on accurate.
The problem with that testing is that to accurately drop test you have to have a very precise rifle/load combo in order to achieve an actual center for your group and it needs to be at least 10-shots. My drop testing was done at 500yds where there is about a .3" difference for each 1% of BC change. Further is better but that error grows with distance as does your drop in precision. Most importantly, if you did this by dialing on your data (vice shooting from a shorter range zero and actually measuring your drop from point of aim) you will likely get errors since most people don't tall target test their optics and do not know what they are really dialing on.
A BC is only good for a velocity at which it was actually tested but those numbers work in velocity bands, some wider and some narrower. As velocity decreases so does the force of drag but the drag coefficient goes up. Because the drag coefficient changes with velocity so do the form factor and BC. Cross component wind does not affect the drag coefficient, form factor, or BC. The problem is that the bullets we use (specifically the Parker, Pittman, and mine not the pistol shaped bullets that like the SST) do not really match the G1 or G7 model well. This isn't really a problem above 2000fps but is underneath that and I would say it is a safe bet that a 300gn offering from any of those listed is hitting that floor by 350yds if started at 2800fps from the muzzle. For those who like light bullets and high MV this is the point where you begin to lose the initiative due to velocity decay and more importantly time of flight (specifically lag time) in regard to wind.
Enter wind. Wind is not like gravity where it can be measured and does not apply equally across the bullet's flight path. It goes across, at angles, has gradients, faster here, slower there, and goes up and down with terrain. Consider that a master class shooter can judge wind to within 1mph in easy conditions and 3mph in difficult conditions. On the other hand a novice shooter (novice to LR and working with wind) can only judge to 3mph in easy conditions and about 5mph in difficult conditions (think about some of the estimations of wind you've seen here on the board). Does it surprise anyone that when shooting relatively low BC bullets that lose velocity rapidly which causes a higher lag time in which the uncertainty of wind works on the bullet, that you think your wind BC is different than your drop BC (which also has some aerodynamic jump due to wind and more of it the faster your barrel twist)? It is not different, it just appears to be because you don't know what the wind is doing.
The key to winning this fight is to practice reading wind and I'm collecting video every time I hit the 1000yds KD range that I'm compiling into one file to show y'all what the Kestrel says at my position, what the wind flags (wind gradient) are doing at 600 and 300yds, and what mirage looks like on the range so you can guess and get an actual answer. To bolster your ability to make solid hits shoot a higher BC bullet that penetrates the air better.
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Post by keith on Apr 1, 2016 14:53:25 GMT -5
Temperature, altitude, humidity and velocity would change b.c. imo! It doesn't actually change your BC but it causes your atmosphere to mimic a change in BC change. Air density and BC are directly proportional so a 1% change in air density has the same effect as a 1% change in your BC. Humidity has less of an effect than temperature or barometric pressure. Altitude is offset by corresponding changes in temperature and pressure. |
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Post by elkman1310 on Apr 1, 2016 17:49:05 GMT -5
Keith I am in the process of building my own target cam system for the very reason you described. Our 1000 yard range can be the hardest place in the country to try and shoot. Our wind flags do not tell the real story as to wind and its affect on the bullet flight path. We now that a right wind on our range will induce vertical dispersion of the group this has to do with the right hand rotation of the bullet Since most shooters are using a right hand twist. But people have experimented with left hand twist barrels to see if they could over come this wind affect. Results were mixed. I want to be able to see my bullets come into the target at 1000 yards and try to find a reliable wind flag indicator to use on our range that's probably a tall order. I know there are target cam systems on the market but I don't need or want all the extra software that comes with these units.
Since this is a M/L board if you would like to talk about this long range shooting more maybe we should move to another post.
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Post by Richard on Apr 1, 2016 20:15:43 GMT -5
I would join in the discussion but it would become redundant since Elkman (Carl) and I are pretty much on the same thought line.
This is why making a good hit on game out beyond 400 yards or so becomes a bit dicey with the bullets we are launching from these muzzle loaders. Yes, under ideal (read my lips--no wind) conditions with a good solid rest and knowing your scope settings at various distances, a GOOD experienced shooter can make lethal hits. The real facts are that most "hunters" do not shoot enough and test enough to accomplish this and therefore should stick to more realistic distances (read my lips............under 300 yard)
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Post by keith on Apr 2, 2016 8:19:55 GMT -5
Elkman,
I don't shoot BR so I'm not sure what your wind flags look like or how accurate they are since your experience mirrors mine in regard to flags; all the BR stuff I've ever seen are pictures of the flowers, spinners, streamers, and other things that make a short range BR match venue look like an Afghan graveyard. The tall wind flags that you see at HP/XC/Palma matches are what we use on the KD range (only on the weekends for match practice because at work there are never flags since they don't exist in the field) and I find them to be "slow" as far as wind indicators go but they do allow you to assess gradient and compare to natural indicators.
I, personally, would not pick a twist direction to deal with wind since wind is not always from one direction and aerodynamic jump is always 90° away from the force imparted with direction of rotation (think about a spinning top). Aerodynamic jump is deterministic (like drop) so can be accounted for. Same can be said for gyroscopic drift (spin drift) and would be the one that I might choose a left hand twist for as it would be most beneficial in the northern hemisphere in regard to Coriolis and canceling effects.
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Post by Richard on Apr 2, 2016 19:57:33 GMT -5
Keith............The Piedmont range I shoot the 600 yard matches at does not have any wind flags per say! A number of shooters will bring some that are of the short range variety and put them out anywhere from 50' to maybe 300 yards. Much beyond that, it is very hard to see and make an accurate determination of the value and direction as they are too small. Most have the typical daisy wheels and vanes with tails hanging down. They really do not give the wind a value but more a direction and intensity. Its up to the shooter to interpret what it is saying. Basically we look for flags to be acting the same way during our sight in period as we adjust our POI on the adjacent clay birds. Then in the few seconds between the sight in period and when we go to the target, we pretty much attempt to shoot as fast as possible within that existing condition. If we are lucky and the condition holds and our gun handling is good, we wind up with a small group..............get caught in a let up or pick up and you generally have a big horizontal group!  There is no way to play the wind since you can not go back and shot at the clay birds to verify a change. And here again, we might be looking at the 50 ft. flag with its tail hanging straight down and the daisy wheel barely turning and yet one of the further out flags has its tail 3/4 out and the wheel turning. So you usually just run with the condition at the end of the sight in period. The short range (50yd. 100, 200 and 300 yard) guys can fire unlimited sighters along with their record shots as long as they stay within the time limit..........so they can play the wind having their sighter target to verify a condition. In hunting and in your work, you don't have that advantage:( I typically fire my five record shots in 40 sec. Some will do it in 25 to 30 sec. (single shot fed) Your gun and bag set up are critical. Also the clearances on your reloads must be such that they fit th chamber properly but not too tight that when you open and close the bolt you are rocking your gun side to side and this means more time to align the scope on the target. You want to be able to just nudge the butt forward with your shoulder while unloading and loading and wind up with the crosshairs very close to dead on. This will allow your speed to increase. We are actually allowed 8 minutes to fire these five record shots! The same deal for the 1K benchrest matches. |
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Post by deadeye on Apr 9, 2016 0:39:26 GMT -5
have not spoke to kyle about this but wonder if he has collected some results somewhat like I ran into prior.
the poll says "always"///that's why I voted no///and I do understand exterior ballistic's & potential human error which will always be present to some degree. we could go much farther into g1-g7+ bullet modules but this would get rather long & complicated.
2011 to approx. 2014 with a 1/22tw pacnor barrel I started out developing loads which started @ 2400fps with a 327mh & ended up @2650fps. the gun would print (even cold bore shot included) @ 200yds .6-.7 moa day in day out.
so after many month's decided this barrel was ready to go long for testing. I put it through rigorous testing & into winds sometimes around 35mph even out in the 500-600yd area. each & every time out started with a couple @ 200yds to verify zero & off to the long fields. most testing was done between 435yds to 650yds. each & every time out wind was constantly checked & carefully shot my 3 shot groups with the wind called to the best of my ability. I live & breathe wind/mirage & test my self daily each & every day etc.
my wind calling is almost always within 2mph,very often within 1mph & rarely but sometimes 3mph with winds up to 35mph accuracy. wind angle- a bit tricky but I'm usually within 10 degrees of wind angle. during these times I was often gauging wind as I shot & often stopped gauged & proceeded on. we know angles/winds/speeds fluctuate from time to time & can get winded/fooled. I understand push & shove/pulsating & swirling can & do happen & done my best to not let one off in these conditions.
I averaged .8-.9 moa over the course of approx. 300+ bullets launched(over 3yrs) from 435yds to approx. 650yds in many wind conditions/angles/temps & yardages in different locations to avoid wind shearing/valley's etc.
I also left my scope on calibrated power & often just held zero wind & let it drift & measured & also used calibrated power reticle holds to verify the scope was true on the reticle accuracy. I continued this over approx. 3 years & even @ speeds @2400fps up to approx. 2650fps always was over compensated on wind both ways at all distance's/all angles within reason no matter what direction/N,NW,SW<SSW,E etc..
so I had a nice collection of measurements & adjusted the wind bc to correspond with my findings.... approx. .580-.590 bc wind was pretty much spot on & still use that today with that bullet. el bc was published at that time as .430 which worked out to approx. 500yds where the el bc deteriorated & I adjusted that eventually to the large collection of drops also. from 500yds to almost 800yds.
not making any sense out of this I decided to do 2 more test 2 different days as far as the wind drift equating to a bc much similar to a heavy .308 185 berger vld published @ .549 bc & proven out of a very accurate R5 .308 I own.
2 times out with winds around 25mph @ 435yds I launched a 3 shot groups out of the .308 & went to work with the .458/327mh load @ 2650fps.
both times the 327mh edged out the 185vld in wind drift & my groups were in the 1.75"-2.5" with the .308 & approx. 3" with the sml 327mh....hhhhhmmmmmmmmm
ok-what could go wrong with my sml testing? I ruled out canting for me to be wrong all along with a wind bc that was 35% above published I would have had to mis read wind by 50-60 degrees/angle consistently & or mis read wind mph by that much or more & I do understand the wind chart as to direction of poi vs. poa.
I have never witnessed this with any other bullet/cf etc as I have spent a lot of time on the long fields etc even in high elevations etc & distance's past 1k+ etc with a lot of calibers from 22-250,.308/7mm & 50bmg.
so in the long run I don't worry about it as mindboggling as it may seem as long as I am in the vital zone. |
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Post by jims on Apr 9, 2016 6:51:34 GMT -5
A lot of time to do all that, thanks for the information. Accurate shooting over all those days, yardages and conditions.
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Post by Kyle on Apr 9, 2016 7:15:00 GMT -5
There are many variables that come into play on the construction of the bullet that have an effect one way or another on bullet flight. Center of gravity and sectional density are huge in my opinion and I am currently studying both along with average muzzle velocities and impact velocities. As it has been stated, many of the .451-.458 bullets we are shooting today may not fit 100 percent into the G1 or G7 model. Rate of twist and bullet rpm are also important factors to consider when choosing a bullet and equally when choosing a barrel for your gun. A bullet's BC is useful for predicting drop and drift only when the bullet is stable in flight.
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Post by keith on Apr 10, 2016 8:02:25 GMT -5
Yeah, sectional density is important because it's important to BC. It also has import in regards to terminal performance. SD and G7 are usually very similar in value.
Center of gravity is important to static stability but it's relation to center of pressure is important to dynamic stability in order to prevent overturning torque. This is, IMO, one of the most critical design aspects in an SML VLD because we are trying to achieve a lot with a bullet that is not optimal. That is to say we are pushing designs to the limit. I think it's why we've seen a few problems over the past few years as guys push these bullets further down range.
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There is no way to play the wind since you can not go back and shot at the clay birds to verify a change. And here again, we might be looking at the 50 ft. flag with its tail hanging straight down and the daisy wheel barely turning and yet one of the further out flags has its tail 3/4 out and the wheel turning. So you usually just run with the condition at the end of the sight in period.
