SPIN DRIFT!....I'm such a dummy

[bigngreen]

I see the argument that spin drift and Coriolis are not worth taking into account because they just get lost in the noise, well in an effort to try to get my "noise" tighter the easiest things to cut out are spin drift an Coriolis. It helped my wind calls since now I can make a decision based on wind being the primary factor.

Shooting large cast bullets at long range with our black powder cartridge rifles we'll crank on 2-3 MOA of spin drift right out of the gate at 1000 yards on rifles that the sight isn't shimmed, that's a little more than "noise".

 

[RDM416]

I started this thread a while back and have paid a lot more attention to spin drift since. I am not a competition shooter, just a hunter who likes shooting critters way out there. From what I have been seeing when ranges exceed 500 yards spin drift becomes more than just "noise".

At 1000 yards my ballistic calculator calls for 6" of drift with the load I am shooting. When shooting my 1000 yard steel plate which is 15" square I will consistently group on the far right hand side of the plate or miss slightly to the right. When I dial 1/2 moa of left correction I will be putting them around the center of the plate. I have repeated this little experiment on several occasions with the same result. With no left correction my groups will always be to the right of center on my gong. I have confirmed this with two different 338s and a 50 cal. at 1000 yards.

In the world of shooting critters at 1000, ignoring spin drift looks to me like either a gut shot or a miss, depending on which way the critter is facing. I may be shooting 6" to 8" groups at 1000, but it is important to have that group centered where I am aiming, not 6" to the right. I have been shooting deer, antelope and elk at ranges up to and a little over 1000 for years. I have always been dialing the left correction in at those longer ranges but only because that was what my actual range results were telling me. I just scratched my head and wondered why all my rifles shot to the right when the range got to be 700+. Then as my original post points out, I realized what I had been seeing and compensating for all those years was spin drift. I knew about it, but had been ignoring it because of all those who say "it is not enough to matter" or it is just "noise". Maybe it is for you, but since I have started dialing in the correction for spin drift, my groups are more consistently in the right place at ranges approaching 1000 yards and beyond.

 

[elkaholic]

I started this thread a while back and have paid a lot more attention to spin drift since. I am not a competition shooter, just a hunter who likes shooting critters way out there. From what I have been seeing when ranges exceed 500 yards spin drift becomes more than just "noise".

At 1000 yards my ballistic calculator calls for 6" of drift with the load I am shooting. When shooting my 1000 yard steel plate which is 15" square I will consistently group on the far right hand side of the plate or miss slightly to the right. When I dial 1/2 moa of left correction I will be putting them around the center of the plate. I have repeated this little experiment on several occasions with the same result. With no left correction my groups will always be to the right of center on my gong. I have confirmed this with two different 338s and a 50 cal. at 1000 yards.

In the world of shooting critters at 1000, ignoring spin drift looks to me like either a gut shot or a miss, depending on which way the critter is facing. I may be shooting 6" to 8" groups at 1000, but it is important to have that group centered where I am aiming, not 6" to the right. I have been shooting deer, antelope and elk at ranges up to and a little over 1000 for years. I have always been dialing the left correction in at those longer ranges but only because that was what my actual range results were telling me. I just scratched my head and wondered why all my rifles shot to the right when the range got to be 700+. Then as my original post points out, I realized what I had been seeing and compensating for all those years was spin drift. I knew about it, but had been ignoring it because of all those who say "it is not enough to matter" or it is just "noise". Maybe it is for you, but since I have started dialing in the correction for spin drift, my groups are more consistently in the right place at ranges approaching 1000 yards and beyond.

Amen! I too wondered why all my rifles shot at least 1/2 minute right at 900-1000 yds. until I learned about spin a coriolis. I can't imagine why anyone would not want to correct for it with all the other things we do to wring out that last bit of accuracy....Rich

 

[Bart B]

I am amazed that these folks whose ammo all has half a minute or a bit more spin drift to the right consistantly dope the blowing wind to 1/4th a minute of exact each and every time. 'Course, if they always shoot when the wind's at 2 MPH or less, then perhaps they could do it.

Even better is the fact they do something that corrects cant to eliminate windage errors for that. And they do it to less than 1/4 degree of arc!

They should contact the US Palma Team's Captain and tout their skills and they'd get a free trip to long range matches around the world every once in a while. But they'd have to coach, not shoot.

 

[paphil]

A few months ago I had a gun rebarreled in 6.5-284 and worked up a good load for it. It could shoot 4 shot groups at less than 1/2 inch at 300 yards. Believe me, you could see spin drift with that gun. I killed 4 groundhogs at 1175 to 1206 yards and used only 5 shots. A couple of months later, I joined the Harry Jones 1000 yard club and shot a 4.21 inch 5 shot group. ( think they have some gimmic the first time you shoot to give you a good group so you get hooked!) Haven't shot that well since but I don't think it is the shooter as much as good equipment. The gun is a long action Sendero with a Hart Barrel topped with a Huskemaw scope. And I do coach shooting as an instructor with BOTW. My goal is to share what I know with anyone that will listen. Canting my scope 2 degrees works for me to eliminate spin drift. Verifying that the crosshairs align with the erector mechanism are an important part of that process. For most people, this is rocket science and they don't want to fool with it but there are some who will understand and try it.

 

[Bart B]

Believe me, you could see spin drift with that gun.

Canting my scope 2 degrees works for me to eliminate spin drift.

How much spin drift does it have at 1000 yards?

What do you use to ensure the scope's canted 2 degrees and not 1 or 3 of them?

 

[Loner]

Amen! I too wondered why all my rifles shot at least 1/2 minute right at 900-1000 yds. until I learned about spin a coriolis. I can't imagine why anyone would not want to correct for it with all the other things we do to wring out that last bit of accuracy....Rich

Elk, It's just a matter of "on" or "off" on the ipod isn't it. I just ordered a kestrel to start
using DenAlt. I've made a few errors inputing current weather and the one number
system is a way to solve it. Hasn't cost me yet as they were still good sight-in shots but
would have been no good on elk. We're staying on an 18" wide plate first shot from 700
to a thousand now. Largely due to wind meters and ballistics programs. I still don't use
Coriolis, maybe I should.lightbulb

 

[paphil]

Bart, the 6.5-284 was grouping about 1 Moa right at 1000 yards. To get the scope aligned , I drew a vertical line on the tin side of the barn outside my shop and also a 3 degree line that intersects with the vertical. I drew 3 degrees before I had a dead calm day and thought I had 13 inches of drift. Anyway I put the gun in a canted position by tilting the crosshair left between the vertical and the canted line.Then I attached the scope level in the level position. The proof of the proper angle is the 100 yard ladder or inverted T with the goal being to shoot 1 inch left of the vertical line with 1000 yards of elevation cranked on the scope. Depending on the allignment of the crosshair and the erector mechanism the tilt can range from 6 degrees left to a couple right. Some scopes are accidentally just right and don't need any tilt. It is just something to think about and like I said earlier, it works for me. For shooting 1000 yd compitition, it doesen't matter, you use sighter shots, but for hunting and wanting the first shot to be right on , it helps !

 

[Bart B]

I drew 3 degrees before I had a dead calm day and thought I had 13 inches of drift. Anyway I put the gun in a canted position by tilting the crosshair left between the vertical and the canted line.Then I attached the scope level in the level position. The proof of the proper angle is the 100 yard ladder or inverted T with the goal being to shoot 1 inch left of the vertical line with 1000 yards of elevation cranked on the scope.

With that setup, you'll have shots at 100 yards going 1 MOA left. As range increases with that much spin drift, the shots will be less to the left as target range increases and finally crossing the point of aim at 1000 yards. Are you going to correct for the windage error by canting the rifle a bit to the right for ranges less than 1000 yards.

I don't think your 6.5-284's got that much spin drift. The .30-06 has about 6 inches at 1000 yards and it's angle of fall and total trajectory axis change is much more than your 6.5. So your 6.5 has to have less than 5 inches of spin drift.

 

[RDM416]

Bart, I do not doubt that you have far greater skill and experience at long range shooting than I do. The question I have is why do you discourage compensating for spin drift? Most programs have the feature. It is a simple matter to turn it on and dial for it. Why start off not correcting for something that is going to induce a 6" error at 1000 yards? It seems like saying since we can never judge the wind correctly, why bother to compensate for it??

I have no doubt that I would get smoked at any long range competition, that has never been my gig. I can say (and provide witnesses for most) that I have killed almost 3 dozen big game animals at ranges from 500 to 1000 yards. I missed 1 elk (several times) in a tricky cross canyon wind. ALL others have been one shot kills.

Maybe I am just lucky. All those shots verifing my dial up chart, practice sessions in the field working on wind reading skills, all those hours on the bench trying to load the best ammo I can, all those gadgets like my kestrel, ACI, level,......etc. don't do any good. I am just lucky.

I am quite sure were I to meet you over a cup of coffee or around a campfire that I would like you. I am very certain you could teach me much about ballistics and long range shooting. What I don't understand is why the competition shooting community seems to have such contempt for the LR hunting community. You BR guys will always shoot better groups. You get benches and rests, wind flags, sighters and fairly level terrain. Us hunters must make a first round lethal hit on a critter that moves a little every time we just get ready to shoot, uneven terrain, typically a canyon with tricky winds. We have a bipod and a beanbag for a rest, are shooting from a rockpile after hustling up a mountain, and somehow (just lucky I guess) still make the shot.

Come on out to S NM in a few weeks and you can watch as a buddy and I cow elk hunt. The plan is to shoot one (or two) at around 1000 yards or so. It could be the day my "luck" runs out and you could have a good laugh and tell me what I did wrong.


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[paphil]

Bart, with that setup the bullet is dead on at 100 yards. It only is left after you crank on 1000 yards of elevation and still aim at the 100 yard bullseye . It will be about 28 inches high and I want it to strike about 1 inch left. Spin drift is there at all distances and this method eliminates most of it. You have to know what your gun does, I've read articles that state the 30-06 drifts 14 inches. It depends on time of flight, BC, twist rate and weight of the bullet. Someone posted that a round ball might drift several feet. All I can do is work with my data for my gun and my only intension for posting here is to help anyone else who is open minded enough to think about what has been said and possibly experiment a little and see if it works for them. The method you talked about , using a vise and following a line on the wall will work to see if the cross hair is not plumb with the scope mechanism but you will not see spin drift without firing a shot. Brian Litz probably has a computer program that would do it but I don't. I just use what I have .

 

[cummin_un_glued]

rdm416 i just done some shooting with my 7mm at 800 yards and the first shot landed 5" right so i gave it 3/4 moa adjustment and the next landed .5" left...later i turned on spin drift in my calc and it shows the same and all i'm using is the android program from applied ballistics

btw you still want to get together and do some shooting?

 

[Tumbleweed]

Speaking of spin drift I've got kind of a strange one for you. As mentioned above in an earlier post I have my spin drift corrected at distance so that I will be slightly left at the closer ranges. With all of this talk of spin drift I re-checked my own spin drift correction at 1050 meters. I shot at first light with a maximum of 1/4 to 1/2 mile per hour winds. I had a flag on the target, at 750 meters and at 500 meters that I could watch before letting the shots go. All flags were down when I shot my 3 shot group that was 9 and 9/16". The group is still centered horizontally at this distance which is what I fully expected. The next morning I decided to shoot at around 740 meters in the same no wind conditions. Same thing, all flags down and shot 2 side by side that measured 1 and 1/2" apart. The thing is that the pair is 1.25MOA left of the bull. So, at 100 meters I am .5MOA left, 740 meters I am 1.25MOA left and at 1050 meters I am centered. This suggests to me that at least in my rifle that the spin drift seems to be an "arc" rather than a straight line value with the most drift taking place in the last 300 or so meters. In other words; if I'm .5MOA left at 100 to be centered and corrected at 1050, in theory I should be no more than .5 MOA left any distance between 100 and 1050. In fact the closer to 1050 the more right my point of impact should be moving correct?

 

[paphil]

The more you shoot long distances, the more you will find that true no wind conditions are really rare ! Even a less than 1 mph that can not be felt and does not move the flags can still move the bullet a half a minute or more at 1000 yards ! I have found it easier to dope a steady, measureable 5 mph wind than a " no wind" . Short shots don't move much in no wind but long shots always seem to move and you never can tell which way they will go.