A quality scope will adjust down to 10 yards. I would not bother with half and half setups. JMHO.
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What's with the Slug Speed fetish lately?
- Thread starter Centercut
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It often happens that one forgets to adjust or have it set at the wrong distance/not have time to adjust during hunting...I've done it...
So having 2 or even more "set" distance options withiut havning to touch anything is a wonderful advantage in certain setups
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It is a popular misconception that higher velocity reduces the wind drift, because it reduces the time of flight to the target.
Wind drift is caused by a sideways component to the drag force on the bullet (aka slug). Any projectile turns into the “apparent wind” (which is the vector sum of the forward and crosswind velocities), and hence actually experiences no “crosswind” per se.
Since the projectile is yawed into the crosswind, the drag force has a sideways component that causes the downwind drift.
The drag on any projectile increases with velocity, and experiences a drastic increase in the Transonic range (Mach 0.8-1.2). Each projectile has a different “drag curve”, but here is the one for the G1 profile, from with the BC(G1) is derived.
Wind drift may be calculated by finding what is caller the “lag time”. This is the difference between the actual time of flight from muzzle to target, and what it would be in a vacuum (with no drag). The latter is simply D / MV (distance over muzzle velocity).
I know this is counter-intuitive, but Ballistics is a well established science, though often poorly understood.
Wind drift is caused by a sideways component to the drag force on the bullet (aka slug). Any projectile turns into the “apparent wind” (which is the vector sum of the forward and crosswind velocities), and hence actually experiences no “crosswind” per se.
Since the projectile is yawed into the crosswind, the drag force has a sideways component that causes the downwind drift.
The drag on any projectile increases with velocity, and experiences a drastic increase in the Transonic range (Mach 0.8-1.2). Each projectile has a different “drag curve”, but here is the one for the G1 profile, from with the BC(G1) is derived.
Wind drift may be calculated by finding what is caller the “lag time”. This is the difference between the actual time of flight from muzzle to target, and what it would be in a vacuum (with no drag). The latter is simply D / MV (distance over muzzle velocity).
I know this is counter-intuitive, but Ballistics is a well established science, though often poorly understood.
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I shoots them where I find the accuracy.
As for the slugs needing to be driven fast to be accurate and if BC is an over blown concept why do some slugs maintain MOA accuracy at reduced speeds down range? Would they not lose stability as they bleed off energy and velocity? Asking because i do not know. Not arguing with anyone.
Bear in mind that scenario is not the same as deficiencies at the muzzle being magnified by distance.
As for the slugs needing to be driven fast to be accurate and if BC is an over blown concept why do some slugs maintain MOA accuracy at reduced speeds down range? Would they not lose stability as they bleed off energy and velocity? Asking because i do not know. Not arguing with anyone.
Bear in mind that scenario is not the same as deficiencies at the muzzle being magnified by distance.
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Well in my case, I go where my bullet and barrel takes me. Unfortunately for my one M3 build, it’s quite fast. Way faster than I wanted but it is what it is. I don’t give a crap about BC or wind drift. All I care about is small groups way down range. You can have the greatest BC on the planet but if your groups are big or inconsistent, well I guess all you have to brag about is how high your BC is. I have always been able to find a good spot with all my slug shooters at 950 down to 800fps. That’s what I prefer. Except one gun. On a positive note I did pop a groundhog with it a couple days ago at 285 yards. Did the guns crazy speed help me? Well with still probably a 15 foot trajectory, probably not. But how accurate the gun is at that speed did.
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I attempted to explain what causes projectiles to drift downwind in this thread. https://www.airgunnation.com/threads/how-wind-causes-pellets-to-drift.1278969/ Time of flight is not the relevant factor, as said before, it is the lag time which is important. A projectile which does not slow down in flight will have no wind drift, no matter how long its time of flight may be.
The problem with BC and wind drift is that a BC for a particular slug which increases as speed increases does not mean that the wind drift is also decreasing. All it means is that the rate of increase in wind drift with increased speed for that slug is less than it is for the reference projectile. This is one of the problems in the use of BC's. It is much more informative to look at the slugs drag coefficient curve with speed, i.e. the drag law for the projectile being used.
It is also possible for two slug designs of the same mass which have the same BC, as calculated by velocity drop, to have different wind drift. This is due to the drag curve shapes being different and different to the reference drag curve. It is just a coincidence that the velocity drop over the measured range is the same.
Unfortunately, in some cases, BC is a very imprecise measure, particularly if the wrong reference drag law has been used or the wrong method has been used in testing.
The problem with BC and wind drift is that a BC for a particular slug which increases as speed increases does not mean that the wind drift is also decreasing. All it means is that the rate of increase in wind drift with increased speed for that slug is less than it is for the reference projectile. This is one of the problems in the use of BC's. It is much more informative to look at the slugs drag coefficient curve with speed, i.e. the drag law for the projectile being used.
It is also possible for two slug designs of the same mass which have the same BC, as calculated by velocity drop, to have different wind drift. This is due to the drag curve shapes being different and different to the reference drag curve. It is just a coincidence that the velocity drop over the measured range is the same.
Unfortunately, in some cases, BC is a very imprecise measure, particularly if the wrong reference drag law has been used or the wrong method has been used in testing.
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While I’m not a ballistic expert, but I know someone that is. So I reached out to Matt Dubber to see if he could elaborate on our discussion. Here’s what he had to say:
“Yes it is true that there are benefits to shooting slower. I spoke about this a bit towards the end of last year’s RMAC PRS video I made. Check the screenshots, the ONLY difference between these two is the velocity, one is 980 and the other is 1080. But check the wind drift, the slower one has less drift. This is because drag increases the closer you go to the speed of sound. You won’t see this as a lower BC because the BC factors in the drag curve of whatever function you are using (G1, RA4, etc) but if you look at the actual drag functions on a graph you will see the spike in drag. That’s why I will always choose a heavier slug at slower speed than a light slug at higher speed.”
“Check how the drag increases drastically right around the 1000fps mark on all the different drag functions. They are all slightly different which is why you should try choose the function which is closest to your actual bullet shape (i.e. you might get more accurate wind drift results if you use a RA4 drag function instead of G1 when using a single BC)”.
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Thanks Michael and Matt. His example is negligible, but still illustrates the point. My question to Matt would be then if the drift is less at lower speeds say 900 to 950 fps, why does he shoot at 980 or higher?
The 40 grain Javelins with 0.137 BC are very good for conventional slugs. But not even close to the 0.21 BC we’re seeing from the Altaros ATP Smooth .25 cal 49.5 grain boat tail or .22 Altaros King 40 grain slugs. His drift is 3.77 MOA, and under the same conditions mine is 2.6 MOA. That’s a difference of about 2.5 inches at the 200 yard example he uses.
One thing that interested me playing with Strelok is the difference in drift for 90 and 270 degree wind direction at longer distances. Using Matt’s 200 yards and 5 mph full value wind, the difference is almost 50% greater drift with 270 degree than with 90 degree wind for a right hand twist barrel. The difference is much more than negligible. Spin drift becomes a significant factor in winds at distance.
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Thank you, Miles, for chiming in!
I had been waiting for your response to this discussion for some time now!
The link you provided is excellent:
How Wind Causes Pellets to Drift
One thing which affects all shooters, but in particular the air gun shooter, is the effect of a cross wind giving downwind drift. Here I will try to explain in a simple way how downwind drift is produced and how it varies with range and speed so that readers may understand better how their...
www.airgunnation.com 
Among all the "ballistic specialists"⁍ it's always good to hear what a professional ballistician has to say ⁌
— one that has the proper training and decades of experience in the field.
I'm so glad that you've come to AGN a couple of years ago.
Thank you for your contributions to this forum!
Matthias
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ok, so heres my questions on this. if all of this is true then what happened to all the variables? you have spin, center of gravity, center of pressure, weight, etc. all are left out of these equations. if pellets or anything yaws in flight then pressure from forward movement will act upon both the tail and nose, depending on where the centers are there will be different reactions by the pellet. a pellet or slug will always try to fly straight and as it yaws pressure will act on the tail to push it back in line. this is also known physics so how does it not apply? using matts statement, he chooses heavy and slow over light and fast. if speed or BC is the answer then why choose heavy at all? the weight of a projectile does not change the force applied on the front, so it should have the same amount of drift if frontal force is the deciding factor. if your reply is that heavy resists forces better, then that works across the board and will be seen as a higher speed at a given point in time.
michael, using those profiles can you tell me what the time of flight for each was? and tell me what the drift was for each at the same TOF
michael, using those profiles can you tell me what the time of flight for each was? and tell me what the drift was for each at the same TOF
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I can’t claim to be a ballistic expert, just relaying what Matt & I discussed last month at NAC.
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I certainly am no expert either as clearly I may be completely wrong lol. just wanted to see what #'s you came up with since you already have those profiles.
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I'm confused by this statement. a projectile is anything that moves through the air so if I fly a plane at 300 mph it is not slowing down or a car at 200 mph however when a crosswind acts on either projectile it will drift off course and continue to drift until either I correct it or the crosswind stops. are we saying this isn't true? or are we saying slugs don't follow the laws of physics?
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Always tuned my guns regardless of slug caliber, shape or weight to 880-920 fps not because of shot count, air usage. shot cycle or anything along that line. The main and only reason is to stick to speed at or below Mach 0.8. At or below Mach 0.8 there is no chance of transonic turbulence forming at the ogive of the bullet/slugs to slightly destabilize the slug which increases drag. If you want ultimate accuracy then stay out of transonic zone, this is decades old knowledge.
And there is NO difference in wind drift between 800FPS and 1000 fps, I tried.
And there is NO difference in wind drift between 800FPS and 1000 fps, I tried.
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Actually, muzzle velocity is a poor indicator of deflection as a stand alone variable. Time in flight is also not a variable of predictable wind drift effect. The. 17hmr screams out the muzzle, only to be buffeted badly by wind. So no, speed at the muzzle doesn't equate to less deflection. The resultant drift is best explained by the down range velocity drop, called "lost time ". A projectile that retains the higher percentage of muzzle velocity as it tracks down range will be less affected than a projectile that looses a higher percentage of muzzle velocity. The "lost time " model compares muzzle velocity from muzzle to target at initial velocity. So at 900fps it would take 3 seconds to travel 2,700 ft. Real world time in flight would take longer. The difference is "lost time ". The less lost time, the less deflection. To illustrate, an example is the 22cal Rimfire in sub sonic compared to it's high velocity big brother. Looking at a ballistics chart, it shows the subsonic to be less affected by wind. Both 40gr, both dealing with 5mph cross wind, both at 100yds. The subsonic has a lower "lost time" percentage. This holds true regardless of projectile type, weight, or muzzle velocity. Airgun or powder it is "lost time ". So yes, it is true: velocity can not, on its own, decrease drift. Bill and Addi
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I hope your car is not a projectile, I hope it is in contact with the ground and thus cannot turn about its CG to face into the combined total wind direction. The aircraft is a projectile and if cruising at constant speed has net-zero drag. All the pilot does is turn the aircraft to face the combined total wind direction, just the same as a slug or pellet does, but, because there is no drag, it does not drift but flies happily to its destination. The pilot is steering a different course into the total wind but compared to the ground the course is still towards the destination.
The effects are most noticeable with artillery rockets. Rockets with sustainer motors do not drift at all in the wind, while a rocket which is accelerating drifts upwind, not down. When the motors cut out, the rocket drifts downwind, just like everything else.
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When the pellet or slug yaws, assuming it is a stable projectile, the yaw will mean it is facing into the total wind direction made up of the projectiles forward speed and the crosswind speed, this is not the same as the direction in which the projectile is travelling relative to the ground. Because the projectile is facing into the total wind, there are no side forces or moments, even though the projectile appears to an observer on the ground to be travelling slightly sideways, as the airflow is the same on both sides of the projectile. You can clearly see this effect when you see aircraft coming into land on a windy day. The aircraft clearly looks to be flying somewhat sideways, rather than facing the direction in which it is going, until the pilot straightens it up just before touchdown.
As for the heavy and light projectiles, say we have two projectiles which are identical in size and shape, but one is much lighter than the other. At the same speed, the drag force on both projectiles will be the same, and both will yaw by the same angle to face into the total wind direction. This means that the same size component of the drag force will be acting in the downwind direction, but it will produce a greater acceleration in the downwind direction on the lighter projectile and thus more drift. The lighter projectile will of course have a much smaller sectional density than the heavy projectile and thus a lower BC which will reflect in the increased downwind drift.
While in this case, Matt Dubber is correct in that it is due to the drag coefficient increase as the speed approaches Mach 1, I am afraid he is not really an expert in external ballistics. Unfortunately his external ballistic videos contain literally dozens of mistakes, some of them very basic which anyone working in aeroballistics would see immediately. It is a pity that he has not seemed to be interested in correcting the worst mistakes, mainly in the video on pellet stability. This thread contains the real explanation for aerodynamic stability of pellets. https://www.airgunnation.com/threads/aerodynamic-stability-of-pellets.1276895/
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According to Chairgun
A 25.4 RDM BC of .05 shot at 820 fps takes .3 sec to travel 75yrds drift 2.52 in
A 45gr .30 BC .038 shot at 848 fps takes .3 sec to go 75yrds drift 3.33 in
So the heavier and faster pellet drifts more. The faster you shoot that 45gr the worse it gets
A 25.4 RDM BC of .05 shot at 820 fps takes .3 sec to travel 75yrds drift 2.52 in
A 45gr .30 BC .038 shot at 848 fps takes .3 sec to go 75yrds drift 3.33 in
So the heavier and faster pellet drifts more. The faster you shoot that 45gr the worse it gets
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980fps is near optimal for that slug at 200yds. If you were shooting out to 300yds, then you could likely do better with a little faster, say 1020fps.
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