Spin Drift at 1500 yards

#51
Re: Spin Drift at 1500 yards

If you have a built in cant, then set the level for that cant, wouldn't if give you the same consistancy?

Tubb sells a spirit level front sight for his Tubb 2000 and level adaptors for scopes.

Before we can work on the spin drift and everything else that may or may not effect the bullet in flight, shouldn't we work on getting rid of all the shooter errors as possible, and inconstant cant is one of those shooter errors.
 
#52
Re: Spin Drift at 1500 yards

Frank,

If your only point is that ergonomic stock design is conducive to a reduction of shooter induced error, then you will get no argument from me.

It is the concept that one known source of human error somehow negates a mathematically correctable drift error that has this thread running in circles.
 
#53
Re: Spin Drift at 1500 yards

I'm not the brightest bulb on the tree ,
Look at it this way , projectile is spinning , air is resistance /friction ..spinning projectile is "grabbing " said friction and will eventually get enough bite to cause it to veer off course , abet its a very minute amount but still there !! .............but hey what do I know about physics
 
#54
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Twisted .308</div><div class="ubbcode-body">I'm not the brightest bulb on the tree ,
Look at it this way , projectile is spinning , air is resistance /friction ..spinning projectile is "grabbing " said friction and will eventually get enough bite to cause it to veer off course , abet its a very minute amount but still there !! .............but hey what do I know about physics</div></div>

I don't think anyone is going to argue that spin drift does exist, from a scientific standpoint of course it does. The point of those above is that factoring in spin drift for your shots is not important because of how minor an effect it will have in comparison to potential shooter induced error, may it be improper trigger control, failure to acheive NPOA, etc, etc....
 
#55
Re: Spin Drift at 1500 yards

This is the problem,

NOBODY IS SAYING IT DOESN'T EXIST !

All I am saying it different shooters have a different effects on the course of the bullet and in most cases very few people are effected in the flat rate way it is presented, they give you an "averaged" number and say, Voila ! this is the answer, which, maybe true in a fixture, but not true for all shooters. One number does not solve the number of problems the person puts into the shot, nor does is it greater than doping the wind incorrectly, so unless you have a person who can hold SUB MOA out to distance consistently, under all conditions and can dope the wind to within 1/2 MPH across the entire path of the bullet there are more important things to worry about, especially for the AVERAGE shooter, who should be focused on the fundamentals.

All to often people on here and in other places prove my point by saying they dial 1 MOA OR more at 600 yards or so for SD and it "works" for them. I have even heard of people dialing SD at 400 yards. We have been given examples of people who dial more than 2 MOA at 1000 yards and call it SD... like above. This is incorrect and when called it all of the sudden I don't believe it exists. They get butt hurt on me calling a Spade a Spade and immediately switch to the all or nothing proposition, as in pretending I am saying something it is not.

Same thing with a Level,

It's a TOOL, it should be there for the shooter to better understand his position. If they set up for the shot each and every time and note the level after settling in on target and it is off, that is a clue. The answer is not focus on the level, while it helps, the answer is to adjust the rifle to you, because you are naturally canting the rifle, but forcing yourself away from that natural inclination is something you should work to fix. But the level is simply there to tell you whether your position is good or not, not to force you into something you won't do naturally. Because, 1. It takes your attention away from your sight picture and target, 2. it changes your position, and 3. subconsciously you will move back to your natural position.

If too many people are blowing shots because the rifle is canted and feel the level is the fix, I would say, we are doing the same wrong we did before only now we trying to divide our attention instead of fixing the ergonomics of the situation. Change the rifle to fit you then level the scope to the fall of gravity with the rifle fit to the shooter. If you don't have the adjustment consider a better stock. So if you want to go, level rifle and level scope you can move the butt plate and cheek piece to account for it, otherwise you will naturally go off center.
 
#56
Re: Spin Drift at 1500 yards

Twisted, that's not actually how spin drift occurs, but the how is much less important that the fact that it does, and it's a correctable souce of error for very little investment of time and effort.

My personal suggestion, if the value of a correction is more than half of the projected group size, or more than twice the nominal aiming error (for most good shooters about .1 mil), then you should probably correct for it. This presumes that the correction will not cost more time and effort than it's worth in results.

For example, tkae an 800 yard shot with a .308, where nominal group size is 1 MOA, or about 8.2". If the target is a guys chest, giving you about a 10" x 14" area to hit, the 4 or so inches of spin is hardly worth the effort. If we were to make the target a head, and only 6" wide, then the maximum chance of a hit means we need to adjust.

Of course, if you can't shoot well, or you just screw up the shot, it matters not at all.

I think the 2000 yard example I posted shows the nature of the problem. Deliberate or not, if you hit small targets at 1200+ yards, you are taking spin into account, otherwise you are missing, even if you CAN actually shoot.
 
#57
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">My personal suggestion, if the value of a correction is more than half of the projected group size, or more than twice the nominal aiming error (for most good shooters about .1 mil), then you should probably correct for it. This presumes that the correction will not cost more time and effort than it's worth in results.</div></div>

Cory, that's excellent advice.

The Infantry School teaches (rifled) mortarmen in the FDC to use the lowest charge and shallowest angle to minimize long-range dispersion. Drift is always added prior to giving gunner deflection changes. If it's not added it's a miss.

Probably makes a bigger difference for riflemen when engaging at the near-maximum range and transonic boundary of the projectile.
 
#58
Re: Spin Drift at 1500 yards

"Change the rifle to fit you then level the scope to the fall of gravity..."...

Frank, you said something very similar once before. If the vertical crosshair is held plumb in this configuration, how do you avoid canting the barrel?

Regarding "average shooters", isn't the point of refinement in technique to make SD, and CE, corrections worth the trouble?
 
#59
Re: Spin Drift at 1500 yards

At the XLR course the computer recommended .4+ Mils for the 338 at most of the targets beyond 1250m, I used .2 Mils for everything and it worked out fine by me, I added it in because I noticed it in the wind drift. The wind was such to equal out the call it required a .2 Mil change in my dope. Anything inside that distance I did not use a SD correction at all.
 
#60
Re: Spin Drift at 1500 yards

Frank, certainly the shooter is the weak link in the system, which is why we have classes in this stuff
wink.gif
.

All of this, levels, spin, ACI's, etc are of little relevance to one who can't execute the firing process correctly.

I've watched students express wonder at how, with wind clearly blowing left to right, they hold left, shoot and miss left, then hold center to hit with a second shot. At this point, I get them to evaulate the position, they see the 5 odd degrees of cant to the left they have in, square up and shoot again with the correct wind call and bang-dink. The wind read and correction were fine, the execution was not. How about that! I love it when a learning moment occurs!

This ELR stuff is easy, it only demands perfection!
 
#61
Re: Spin Drift at 1500 yards

Noel

Do you indicate and time your barrels ?

or better question is, how many people out there have an indicated and timed barrel that the Center on it is set to either 12 or 6 O Clock ?

Why don't you call David Tubb or McBros and ask how the Tubb 2000 works with the 0, 5, or 10 degree cant settings ?

Direct quote from the McBros site:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The action features a full-length picatinny sight rail that will accept an almost endless array of competition sights and scope rings. <span style="font-weight: bold">The action's adjustable sight mounting system allows the sight rail to be mounted at one of three pre-set mounting angles – 0, 5, and 10 degrees – to allow the shooter to cant the rifle while shooting and maintaining a straight-up level sight. </span> All barrels come standard with the muzzle turned down to accept a clamp-style front sight mount, barrel extension, or cant indicator.</div></div>

Again some people would call that a clue,
 
#62
Re: Spin Drift at 1500 yards

Noel, it's just like the offset sights on a Vickers or Bren gun. There, the POI was just offset to the right by by the bore to sight distance, about 2". At 1K, you are still 2" right, but who cares?

Rolling the scope in the rings to accomodate the shooters built in cant is way less than that. In this case, the amount you are offset to center bore is not much more than the diameter of the projectile, unless you are going rollover prone or something. The zero point is less than a click out of square, you can't see it no matter the range. You just have to get the same position every single time, same as if you want to be vertical plumb.
 
#63
Re: Spin Drift at 1500 yards

Holding a rifle canted with a "plumb" scope/reticle is the same thing as having a plumb rifle with a canted scope reticle.

Both are incorrect.

That is all.
 
#64
Re: Spin Drift at 1500 yards

Frank,

Yes, I do index barrels.

There is a difference between the operation that you described, and rotating a zero degree rail on a non-canted action. One extra correction is required for the latter, but is linear (and simple). The former *guarantees* a cant error (if your technique is good).
 
#65
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">The problem is, and I know everyone & their brother can debate what the books and computer says, but the<span style="font-weight: bold"> "human factor"</span> overrides anything calculated for drift.

Anytime I have spoken to any one about data collected from a fixture shoot versus shot by a human it doesn't line up... taken that one step farther.

At a class we zeroed a rifle in a mechanical rest @ 100 yards. The rifle was zeroed to the scope with as little Human input as possible.

We then had 10 students from the class shoot at 10 1" dots at 100 yards to include 1 left handed shooter.

The results were 4" of horizontal variation from shooter to shooter. Some hit the 1" dot, some hit as far as 2" to either side to include the left side. So once you figure in the <span style="text-decoration: underline">human factor</span> your personal <span style="font-style: italic">"Shooter drift"</span> can easily add too or eclipse the recorded (calculate) SD. So saying that a bullet will drift 9 or 10 inches from center at 1000 yards is great, but without knowing the Human Factor Calculation or Shooter Drift... you're guessing. Also without knowing the "exact" twist of your barrel, and not what the manufacturer says, but what it really is, you can easily be off as well. If the program you are using does not calculate the stability factor and is not adding in the twist rate, all it is doing is giving you a flat rate that falls within an area they hope you won't notice.

Does it work, sure, but the <span style="text-decoration: underline">Human Factor</span> is bigger than both SD and Wind in 90% of the cases out there, so saying 1 MOA works for Bob, Joe, Bill, Tom, Steve, etc simply doesn't work. Which is why there is so much debate. </div></div>

Anyone in question/debate about spindrift should re-read the above post. Lowlight nailed it.
 
#66
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Holding a rifle canted with a "plumb" scope/reticle is the same thing as having a plumb rifle with a canted scope reticle.

Both are incorrect.

That is all.</div></div>

if you say so, the new DTR reticle from David Tubb comes with very detailed instruction, the first line of those instructions are:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Level your DTR scope to your natural position. The Horizontal stadia lines will indicate the scope has been leveled.</div></div>

Like Cory said is less than a bullet diameter and if you can see that, well you're a better shooter than the rest of the world.
 
#67
Re: Spin Drift at 1500 yards

I think that we are missing some information. Are you talking about a recticle matched to a Tubb rifle system, or a scope that you can mismount on any rifle with no adverse effects?
 
#68
Re: Spin Drift at 1500 yards

Noel, let's presume the base and barrel are all nice and square to the stock. The shooters natural position puts them in a 5 degress right cant. So, the scope gets rolled in the rings 5 degrees, so it's plumb when the shooter is in position.

Over a 2" scope to bore height, the puts the reticle about .2" off the centerline. So, technically, you need to zero .2" left of actual center to be parallel bore all the way out, but you'd need to be shooting .1" groups to tell.
 
#70
Re: Spin Drift at 1500 yards

Nope, forward cant is not relevant. The front rear slope in the base means almost nothing. Figure a 60 MOA base is 1 degree forward slope. Somebody can do the math, but if you roll the rifle 5 degrees, you'll move the scope centerline some fraction of a MOA off the bore centerline, and in a direction that would acutually take out some of the horizontal offset. Someone better with trig would need to diagram that and run the numbers.
 
#71
Re: Spin Drift at 1500 yards

I think we should just drop the discussion of the adjustments and do 1 or 2 things differently...

Zero all our rifles at 9:00 on a 1" dot,

zerotarget.jpg


and

Use only Left hand twist rifles in the Northern Hemisphere for any shooting beyond 800m.

Then we can all stop worrying about it and just focus on the fundamentals. Instead of these distractions. Sure the cant will still be around but at least we can cut out a good portion of the conversation and at least steer it back to act of executing the firing task.
 
#73
Re: Spin Drift at 1500 yards

.2" off centreline... zeroed at 100... so .2 the other side at 200... assuming that that offset increases at the same rate wouldn't it only be like 1" offset at 1000

I don't believe in levels, find that they force you into unnatural shooting position. fine shooting f-class or BR with minimal contact with a 20lb rifle, not good for field shooting. prefer to shoot rifle as it feels natural to me and have reticle level with earth from there. so I get some minute offset between reticle/bore. haven't noticed it yet.
 
#74
Re: Spin Drift at 1500 yards

But we're off spindrift now.


My feeling is that if I'm hitting without correcting for SD <span style="font-style: italic">at a range where it is significant</span> then I am doing something "wrong"


I need to shoot more past 800-1000meters to gather my own data on this I guess.
 
#75
Re: Spin Drift at 1500 yards

Offset of the sights on the gun makes no difference. Sights on a 4.2 or 120mm mortar, 105 or 155mm howitzer, rifled 120mm tank gun, or 16-inch naval rifle aren't in-line with the bore -- they're off to the side.

The projo will spin in the direction of rifling twist (right twist-right drift; left twist-left drift).
 
#76
Re: Spin Drift at 1500 yards

The offset is less that the value of a 1/4 moa click. If you get your windage zero confirmed at say 300 yards, it's parallel bore, and no factor at all. It just stays constant .2" off center, less than a bullet diameter.
 
#77
Re: Spin Drift at 1500 yards

If you have .2" horizontal offset say to the left at 0meters, 0 offset at 100 meters because you are zeroed, then it stands to reason that you would have minute offset to the right past that?

but as stated the figure is so small as to not matter even remotely. I'm never going to notice 1" at 1000 meters
 
#78
Re: Spin Drift at 1500 yards

After reading all the previous posts I can't wait to someday find a range with such perfect conditions that I can calculate all of this in and be perfect on that first shot. The main range we shoot at for the long distant targets are from one hilltop across anywhere from 1 to 3 valleys with treelines scattered across the hills and into the valleys. Some arch higher than the trees and then back into a far field. We sometimes see 4 different directions of wind on one target looking at treetops and grass in the fields. On a lot of our farther stages the wind flag can be flying straight out to the right. What you are seeing is heavy left to right wind and you should dial or hold left. You won't even be close, somewhere in between you and that target is wind the opposite direction. Looking thru the scope your mind is saying this isn't right.

Yup, SD and other scientific things I can't even remember probably are real but at least for me that is the least of my worries when making a wind call and adjustment on that shot. This is just a small part that affects our shots even if we do get everything else pertaining to the human element perfect. We've managed 1 perfect windless day at Rayners and that day me and my son both held center holds to 1000 and got hits with no SD adjustments or windage adjustments. Since we're only shooting to 1000 yards and don't have the equipment to stretch it out we haven't needed to explore the infinite things that are such a small factor when based on much larger factors that affect our bullets to our intended target.

Topstrap
 
#79
Re: Spin Drift at 1500 yards

Nice post topstrap.

Most all of this discussion is purely academic. When in field conditions, I don't give spindrift a first thought, nevermind a second.

For academia sake: My home 600 yard square range often provides nearly ideal wind conditions, as it is a narrow alley totally bordered by tall mature trees. It is known to be one of the easiest ranges in the midwest.

With a gnats ass zero at 100 yards, it consistently takes me 1/4 moa windage (on an ideal day) to get nicely centered in the X ring. I have a USO level on my pic rail and use it. My Bender scope was setup with the feeler gage method, and it tracks along a vertical line from my zerostop to 76 moa up, on paper, at 25 yards, with USO level reading plumb for each shot.

I assume the 1/4 moa windage correction I need at 600 is on account if spindrift, but calculators say it oughtta be more...? Don't know, care little.
 
#80
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Nice post topstrap.

Most all of this discussion is purely academic. When in field conditions, I don't give spindrift a first thought, nevermind a second.

For academia sake: My home 600 yard square range often provides nearly ideal wind conditions, as it is a narrow alley totally bordered by tall mature trees. It is known to be one of the easiest ranges in the midwest.

With a gnats ass zero at 100 yards, it consistently takes me 1/4 moa windage (on an ideal day) to get nicely centered in the X ring. I have a USO level on my pic rail and use it. My Bender scope was setup with the feeler gage method, and it tracks along a vertical line from my zerostop to 76 moa up, on paper, at 25 yards, with USO level reading plumb for each shot.

I assume the 1/4 moa windage correction I need at 600 is on account if spindrift, but calculators say it oughtta be more...? Don't know, care little.</div></div>

Zero Left ... Dial Nothing !

zerotarget.jpg


So says Stormageddon Dark Lord of All !
 
#81
Re: Spin Drift at 1500 yards

Sinister, et. al.

"Offset" is not the same as being "(non)inline", which is the problem with disregarding scope base angle in "offsetting" an optic.

The whole concept of ergonomic design is sound, but the idea that you can simply rotate an action in it's stock, without other consideration, is not... even if the crosshair is replumbed.

... This thread deviated from the topic the moment SD was dismissed as a factor in an ELR error budget... sometimes reasonable discussion does that.
 
#82
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">"Offset" is not the same as being "(non)inline", which is the problem with disregarding scope base angle in "offsetting" an optic.</div></div>

I concur -- these discussions ALWAYS go ring-around-the-rosies after the first response post.

The overwhelming majority of shooters even in this forum will never shoot to the maximum range of their weapon and optic; if they try, most will not understand their drift error -- they'll either correct and apply corrective action or just spot fall-of-shot and correct from there.

Lots of emotion, little critical analysis. I don't know why it's such a charged topic -- artillerymen and rifled mortarmen have been applying it for many, many decades. Hatcher wrote about it around the turn of the century using the 30-06 as the test platform.

Just one more point to recommend "Shut up, go outside, shoot it and see." Stop the foot-stamping and prove it to yourself.
 
#83
Re: Spin Drift at 1500 yards

Noel, try going out and shooting it, instead of sitting there trying to crunch a number on your calculator... it's not the same.

The tiny bit of rotation is barely perceivable, when you consider how little you actually move it is ridiculous to think it helps, but believe me it does and having shot a bit beyond 1000, it doesn't have an ill effect.

Absolutely, the optimum way to address it, is to get a stock that actually adjusts to the shooter, look at the Olympic small bore / air rifle crowd, they angle, adjust, cant and move the rifle in so many way it will make your head spin to give the shooter the best possible advantage.

Forget the fact, like Sinister said, that 85% of the people who own a rifle of this type out there will never shoot it to distance, even then they barely shoot it to it's capabilities inside those extreme distances. If I am shooting High Power / F Class, etc, I can turn the rifle on it's side and just "zero" for range and as long as I can repeat it consistently every time it doesn't matter. I can hit what I am aiming at. The difference is taking it beyond and shooting unknown distance stuff, so a guy who very little experience with that will be hard pressed to understand the differences. Even with a Palma crowd, having a level on a rifle shot from a sling is smart from a consistency standpoint, but my first thought would be to design a better stock, without a better stock, a level is a good choice. Sling support is difficult a level will help. But on a bipod, if you can't figure out a consistent position then the shooter needs some work, and the level will tell them something, like where to go to fix the position. The SD stuff, if people read my posts, I have never said it doesn't exist, I just find it doesn't work the same for everyone and I generally don't see it in my own shooting until beyond 1250m and then about 1/2 of what the "books" say I should be using.

 
#84
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Noel, try going out and shooting it, instead of sitting there trying to crunch a number on your calculator... it's not the same.
</div></div>

Win
 
#85
Re: Spin Drift at 1500 yards

There may well be some SD but as said I would think with all the other factors it is lost in the judgement/call.
Take a line of guns all shooting with zeroed rifles and see what each is clicking for at long range. Even those V bulling have quite a range of adjustments that just proves no two shooters or their combinations do it quite the same way. Its the reason ballistic calculations get you close; the rest is up to the shooter.

I think those giving advice are right in saying that SD is just too fine a measure to get overly worked up about and as no two shooters are the same any measurement just cannot be taken as gospel.

Get a line of guns and watch the spotters of their first rounds down range. Few give it enough as you need real confidence to click in a lot. Watch the rest of the practice and see the spread; shows you quite dramatically what a drop in wind will do. Any SD will be lost in the spread and be just as likely to add to the error than fix it.
 
#86
Re: Spin Drift at 1500 yards

Inputting spin drift is a waste of time without a level on the rifle.
Place a piece of tape over your level. Then go and set up your rifle for a shot past 1000 yards on sloping ground where the horizon is made up with hills and mountains.

Then remove the tape and see how far off (true) level your rifle is. The uneven ground and the optical illusion of the mountains and hills in the background can give an untrue reference line for level. A level on your rifle is a tool just like any other. It is how you use it that matters.

Field shooting is not like shooting at a rifle range or off a bench. You have grass, dirt, rocks and ants that bite you on the junk to deal with. It is hard, but it is a shit load of fun. Adding in spin drift just adds another interesting dimension to the fun. Its nothing to get stressed out over though.
 
#87
Re: Spin Drift at 1500 yards

We all walk upright, how can you not look at your reticle and tell if it is straight up and down ?

I shoot in the mountains on uneven ground all the time, and I have not found I need a level to tell, I simply look at the reticle, also if you can't "feel" the stock in your shoulder is off, you haven't been shooting enough... who levels to the horizon, heck half of the shooters are so zoomed in magnification wise, they don't see much beyond the target. Quarter the target, enough said. the horizontal line is all you need to know, is one side higher than the other ?

I get it, it's a tool that helps, but if you can't see, you have bigger things to worry about.
 
#88
Re: Spin Drift at 1500 yards

I do walk upright but I shoot laying down.
All I'm saying is try this simple test.
Sometimes you may be set up level, some times you may not. But without a level you will never know for sure.
If your happy to live without one, that's fine. For me I like them.
 
#89
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">.. who levels to the horizon, heck half of the shooters are so zoomed in magnification wise, they don't see much beyond the target. </div></div>
This is an interesting thought.
How do you do your initial set up? I try and set my bypod legs up so that the rifle is level on a cross slope. ie one bipod leg is longer than the other. I do this by looking at the environment around me, the slope, the horizon etc to get some reference for level. I then fine tune the rifle for level when laying behind it, using the bubble level just prior to taking the shot. Stock possition has already been taken care of at this stage and only minor level adjustment is normally needed.
 
#90
Re: Spin Drift at 1500 yards

Interesting conversation. I'm mostly pretty good about being level but off a cheap bag when the target is not level it really drives me nuts because i see the reticle vs the horizontal of the target and I keep wanting to make them level naturally.
 
#91
Re: Spin Drift at 1500 yards

I look at the reticle and see what it is like,

We may shoot from the prone but we still have little levels in our ears that tell us if we are off balance, not to mention I can "see" if the level is off, I am not trying to level to the slope of an uneven ground, I am looking at the reticle to make sure it is straight up and down, or level horizontal.

I don't know anyone who levels off the sky or ground, say shooting even at 100 yards, they are focused on the target and who the heck levels the target on the board a head of time ?

I just know what it feels like in my shoulder pocket and I know what level "looks" like in the reticle... the reticle was leveled with a plumb line, if not the feeler gauges, so it's straight. Odds are, because I am right handed I would cant inboard and not outboard, so I am sure how my cheek weld feels to not cant inboard.

On a different note, I also shoot my right hand zeroed rifles with my left, and I have no change in zero, i can hit in the same place... so clearly I don't need a level to do this and never have, I must have an internal level.

But then again, in 7 years of working in South Texas I never wore sun screen even once, my Olivine skin keeps me from burning, and the girl here always asks how come I hardly ever wear sunglasses, because my brown eyes are accustom to the sun, so to each their own.
 
#92
Re: Spin Drift at 1500 yards

I shot without a level for years and years. I agree we walk upright and are pretty good at getting our level right. I did find that with a sticky bipod you could get it wrong in a rush especially with a GPMG. You knew you had set up wrong as after the first few shots you had to readjust. Shooting with a sling its quite usual to have a cant built into how you shoot a rifle but that is intentional and you make allowances. I found with larger heavier rifles that rely on a bag or bipod they are less responsive and will sit off at an unintentional angle. They are a bit dead. For lighter rifles that are more lively you are more attached to them in the hold so they tend to give better feedback.

However, I have a level fitted at present and in open country I was surprised how often I wasn't quite so perfect as I thought. The fall of the land and where the light was coming from can play tricks once in the prone. I found the level didn't lie. Having said that at the ethical ranges I now shoot I was always near enough if not spot on, and its not a big issue. So, if only for confidence sake, now that I have a level, I don't mind having a quick look as I get into position and into the sighting cycle.

Its not a big deal and there are other indicators such as most targets are upright as are game if you know how they stand with their centre of balance. This becomes pretty natural once one is in the aiming zone and doing all the checks before taking up the trigger. Its the reason I like a plex or at least a vertical and horizontal with a reticule.

Setting your rifle properly as you go down is probably the more important; that and to get behind it correctly so you are comfortable.
 
#93
Re: Spin Drift at 1500 yards

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I know what level "looks" like in the reticle...
</div></div>

Frank,

Perhaps you are uniquely gifted. Or in a small minority. Seriously. Just because you can, does not mean it's necessarily "normal".

My second career after years of engineering was high end (2-8 million $ homes)finish carpentry. I have an outstanding eye for level. I had to. With it I have won many bets over the years with other smartass carpenters, verified with Stabila levels (carpenters are as bad as shooters). And I DO get fooled in the field sometimes. Not often, but often enough to make me aware of the potential.

I found the prudent thing was to use the appropriate instrument. The funny thing is, when I stand behind guys who have levels on their rifles, they're often off.
wink.gif
They don't help unless you check.

But then, this thread was about spin drift... not levels. So back to our normally scheduled programming.

John
 
#94
Re: Spin Drift at 1500 yards

Well I don't know what I have for documentation at present is this:

18.5" Gladius, 800 yards, to Target, on uneven terrain in the mountains, believe me the position is jacked and I had to support my body with my packs to get close to something respectable. you can see them stacked under the rifle to hold it up.
Not seeing a horizon to work off of here...
Screen-Shot-2012-02-03-at-10.09.09-PM.png


The three shot group at the top was mine, the one in the center someone else...

So, where is the horizontal dispersion, and do I need to worry about cant considering this is just a 308 in the open with all that goes into it. Factory 175gr stuff.

Screen-Shot-2012-02-03-at-10.10.04-PM.png


What is that like 5" with a bit of vertical being my worst offense... this is pretty common for me, use the bolts for reference to the group size.

Another group, again 800 yards, testing a load sent to me by Andrew McCourt for evaluation, 21" rifle

McCourt130gr.jpg


I'm not seeing where the level is gonna improve on that... 1/2MOA all day at distance.

My 300 yard group was pretty nice showing that my focus on the fundamentals and not distracting myself with things I feel are controlled by my position

Same thing more McCourt Load development, grouped at same outing as the other on paper, the first round was to make sure I was on the target I did no zero the gun, I was shooting multiple loads out of the same short rifle.

5-shots 300 yards with the 1st at the top for verification on paper.

McCourt139sc.jpg



Focus on the fundamentals, build your position and actually "look" at the reticle and there is a lot more good than bad that will happen.

Trust me, unless you go to gun quickly after looking at the level, if you even think about fine tuning your position your body will move and go to a natural state, if you keep making "level" your unnatural state, you will adjust it back, and be off. Liked noted above, you see people with level "off" level, So by making my rifle fit me and my natural state, my default is level, and my work downrange shows it. Can I rush and blow a shot, absolutely but that is all about no "pushing a bad shot" and nothing to do with level.

Perfect practice builds a better swing.
 
#96
Re: Spin Drift at 1500 yards

Its nice shooting thats for sure. Being a bit tough/critical: I would have liked to have seen two groups, one from two positions to see if moving position had any effect on the POI, even if that was just one group, move away from the gun, and then go back to it for a second group. I also have reservations of any group not on the aim mark. If its not on the aim mark then a group just shows how close all the calculations have got on that particular string of shots. Do the same twenty minutes later and can you repeat it to the first POI? Don't get me wrong its good shooting and I'm not saying I can do any better. Its what I strive for.

This thread was on SD allowance and now with some rifle vertical. Both to remove minor variables that can but only be an advantage. However, I think our conclusion is that they are so small that they are lost in the bigger picture.... wind calculations etc.

I know I quite like my level as its positioned just right and can be looked at as I do my turret, parallax and cosign checks. They being correct I'll then get into my scope picture and won't be looking at them again. I may well twitch to get my perfect sight picture anyway, so I'm no slave to it. Here is my scope set up:
http://i820.photobucket.com/albums/zz128/Muskett_2009/IMG_4328-1.jpg

I do think with the heavier rifles, well when I used to shoot an AI, setting the rifle down on its bipod in line with the target was important. For once put down and bedded then it was a bit late once you had got down behind it to make big adjustments. Heavy rifles you tend to get behind the rifle whereas lighter rifles you move them to you. At the end of the day you want a natural comfortable position. Its the bipod stuck to the ground thats the problem which is probably why I quite liked shooting off the top of a bergen/pack without using a bipod. Having said that the trouble with shooting off a pack is getting stability from the elbows. It takes some right old wriggling to get that good firing position so that you can but just concentrate on making a good shot.

The benchrest boys use levels and may well account for SD and I won't argue with them. However, there is a difference between screwing a group down to benchrest level and getting solid hits on the open hill.

Fun isn't it.

 
#97
Re: Spin Drift at 1500 yards

Nice 300-yrd group but the thread is about SD at 1500.

If you are shooting at 1500 yrd, are confident you have nailed the fundamentals of trigger, cant etc and are confident in your wind calc...would you or should you adjust for SD ?
 
#98
Re: Spin Drift at 1500 yards

Frank, Sinister,

Thanks for clarifying the importance of offset sight alignment when shooting ELR at varying distances. It was suggested at one point that such a consideration was "irrelevant". This, along with a general distrust of mathematics, was coloring this thread with a tint of mystery that seems wholly out of place in a field governed by commonly understood physical laws.

I agree that SD is not accurately predicted with current software... for a number of reasons.
 
#99
Re: Spin Drift at 1500 yards

Noel -- no problem.

Your earlier point about parallax error is right on. At extreme ranges (1,000 to 2,000 meters) we're looking at the projo's drift due to spin imparted by rifling, and the actual physical location and attachment of the sights has smaller effect than the actual flight physics of the bullet.

Sights on an artillery piece, rifled mortar, tank gun, or naval rifle aren't attached to the barrel but may be on a part of the gun's "Receiver," carriage, bipod, or turret. On some howitzers and guns the sights may be removed before the gun is even fired. Leveling bubbles keep the gun oriented to some other fixed object (such as aiming posts) to ensure group consistency. Mauser-style turn-bolt rifles have been around over a century without built-in bubbles.

Even in artillery and rifled mortars drift isn't huge -- but if you don't account for it you'll be off.

fig2-3.gif


fig2-4.gif


That doesn't mean much in the grand scheme of things but "Red Legs" (artillerymen) in the 21st century are proud of their ability to put a 97-pound 155mm HE projo into a dumpster from miles away and over-the-horizon (from a moving ship, tank, or circling AC-130). Surely we can do the same with a .338 bullet that still has plenty of ass behind it going through 2500 meters, fired from solid earth on our bellies.

partc-12b.jpg


<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">For a given range, the drift of small projectiles will be greater than that of large projectiles. For instance, at a range of 15, 000 yards a 5-inch projectile drifts about 250 yards, whereas a 16-inch projectile drifts only 50 yards. The amount which a projectile will drift at a given range has been determined experimentally, and accurate information is available to assure that the necessary corrections to the gun traverse settings can be made.</div></div>

As Cory pointed out a humanoid-shaped E-type silhouette is approximately 20 inches wide. If the middle of your groups drift 15-20 inches right at 1500 to 2,000 Meters (even with everything dead-nuts straight, level, and consistent) in "No winds" you're going to miss to the right.

Good software can make the difference. "Back in the day" mortar and artillery fire direction controllers used charge tables to determine the best charge, elevation, and drift to apply to firing charts or aiming circles to put the projo on target. True plain applied science. I recommended to the US Army Special Operations Command Force Development guys that the next generation 20-shot .338 ammo box should have a generic drop table for standard met conditions on the back along with drift correction. Load magazines, put the table on your sleeve or tape alongside the receiver or scope and go.

This is one of my colleagues showing off hits on his first-ever ELR training day shooting at 1700 yards:

2wmhwl5.jpg

2pyytnb.jpg
 
#100
Re: Spin Drift at 1500 yards

Do suppressed fire, as in machine gun on tripods, give anything for SD? Often as not its 7.62 out to 2200m to give a beaten zone. Or due to the required effect wanted SD would be irrelevant?

I know mortar men give something for the spin when they lob them in at range.
 
You must log in or register to reply here.

Similar threads

702lineman
Head and tail wind effects on elevation adjustments
Replies
9
Views
593
Taylorbok
Taylorbok
U
Short Range Tall Target Test
Replies
8
Views
532
USMC22
U
M
9mm Luger - Windage Drift at 100 yd questions?
Replies
25
Views
619
Devildog
Devildog
pangris
Review of Roaming Shot Range (1000 yard facility) Slaughter, LA
Replies
13
Views
732
pangris
pangris
O
Organizing DOPE
Replies
3
Views
584
Trigger Monkey
Trigger Monkey
Top Bottom
Back
Home
Forums
Merch
Alerts