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

[RDM416]

Well, well, well..... old dog learns new trick. I've never really paid much attention to spin drift. Over the years I have seen a few threads come up that asks about it and it seems the normal reply is that it "don't matter much"..... "too small a deviation to worry about", so I have always just kept the spin drift calculation turned off on my ballistics programs and ignored it. Why complicate things further if it is too little to matter???

I picked up a copy of APPLIED BALLISTICS FOR LONG RANGE SHOOTING (Bryan Litz) a few days ago. First, I was just browsing the book before settling in for a real in depth study and happened across the chapter on "gyroscopic drift". Bryan makes a few statements about how it is "subtle" effect, "extremely difficult to measure", so with my false security so confirmed, I moved on in my scan. At the end of the chapter I see a chart of the drift of a 750 grain .50 cal Amax out of a BMG. I have a 510 AM and that is the bullet I shoot so looked at the chart and it showed at 2500 yards the spin drift is over 81". NO WAY!, I thought..... at 1000 yards the chart shows almost 7". Now I am curious. I go fire up 4 different ballistic programs I have that do spin drift (including the one that comes with Bryan's book) and find much to my surprise that my favorite loads for my .338s all have 6" to almost 8" of spin drift at 1000 yards!!!

I have noticed for years that as I move out past 500 yards my groups tend to drift to the right.... the longer the range the further right. I typically have a little "left to right" wind on my range so I blamed that, and I got really obsessed about making sure my scope was level. Still, to ring my 1000 yard gong I kept having to dial .5 to .75 moa left windage correction in.

Now I know, spin drift is NOT something to be ignored. Not at ranges further than 500 yards anyway. I feel like such a DUMMY for letting this get by me for so long!!

 

[ReachnOut]

No dummy RDM ...... you're probably 1 in 10000 shooters that has ever researched gyroscopic drift and actually know what it is! Fortunately, I trained for many years with the old timers from the long range 'Nam era who incredibly figured all the variables of long range shooting in their heads without the benefit of the iPhone ballistic programs that I use today. Ask someone today to read a mirage and watch them get a blank look.

Actually, it's kind of fun to play around with "spin drift". If you have the range that will accommodate it shooting a 3 shot group every 100 yds from 4 on out really emphasizes the whole drift phenomenon. I've found that if you limit the test to a zero wind day that each rifle and the same rifle with different bullet weights make a significant difference. For my "money gun" on friendly hunting shots or ringing the bell out to 1k the actual drift is 1.5" every hundred past 400. Most of the time I figure my wind, add or subtract the drift depending upon wind direction and let 'er rip.

 

[Boss Hoss]

I have posted on this many times in the past here on this site. You can do a search about it---not rocket science but just simple physics.

http://www.longrangehunting.com/forums/f28/horizonal-stringing-66172/index2.html

 

[Trickymissfit]

Well, well, well..... old dog learns new trick. I've never really paid much attention to spin drift. Over the years I have seen a few threads come up that asks about it and it seems the normal reply is that it "don't matter much"..... "too small a deviation to worry about", so I have always just kept the spin drift calculation turned off on my ballistics programs and ignored it. Why complicate things further if it is too little to matter???

I picked up a copy of APPLIED BALLISTICS FOR LONG RANGE SHOOTING (Bryan Litz) a few days ago. First, I was just browsing the book before settling in for a real in depth study and happened across the chapter on "gyroscopic drift". Bryan makes a few statements about how it is "subtle" effect, "extremely difficult to measure", so with my false security so confirmed, I moved on in my scan. At the end of the chapter I see a chart of the drift of a 750 grain .50 cal Amax out of a BMG. I have a 510 AM and that is the bullet I shoot so looked at the chart and it showed at 2500 yards the spin drift is over 81". NO WAY!, I thought..... at 1000 yards the chart shows almost 7". Now I am curious. I go fire up 4 different ballistic programs I have that do spin drift (including the one that comes with Bryan's book) and find much to my surprise that my favorite loads for my .338s all have 6" to almost 8" of spin drift at 1000 yards!!!

I have noticed for years that as I move out past 500 yards my groups tend to drift to the right.... the longer the range the further right. I typically have a little "left to right" wind on my range so I blamed that, and I got really obsessed about making sure my scope was level. Still, to ring my 1000 yard gong I kept having to dial .5 to .75 moa left windage correction in.

Now I know, spin drift is NOT something to be ignored. Not at ranges further than 500 yards anyway. I feel like such a DUMMY for letting this get by me for so long!!

a good rule of the thumb is that for every .0001" in error with the C/G of a bullet; you'll see 3/32" at 100 yards
gary

 

[Augustus]

Well its good to see folks are beginning to wake up and smell the coffee. I got run off over at snipershide a couple of yrs. ago by the illustriuos( Frank ) for suggesting such a thing existed. I think even he now admits it exists but maintains it just isnt worth worrying about.

 

[Michael Eichele]

You are no dummy. We all 'let things slide by us' from time to time. For whatever reason we ignore it because we have never had to deal with it or there was some other variable cancelling it out. Sometimes we are just so overwhelmed with all of the varibles to factor in and we are frustrated with finding a good load etc etc..... that we are to fried to take on anymore 'problems'. It's called human nature. Welcome to the human race!!

I am glad you realize now the value of spin drift. It still suprises me that so many of the members here think its all a myth. That it is the product of a canted scope or unknown winds etc....They are only fooling themselves and setting themselves up for failure.

Thanks for sharing.

M

 

[Long Time Long Ranger]

Augustus, I wouldn't worry to much over the idiots at snipershyde blasting you. I went over there one day to look around and I can see where a guy without very much experience could get caught up in the BS over there. But a guy with quite a lot of experience can see immediately many of the guys that try to run that forum seem to be young kids and have a lot to learn.

 

[Rocky Mountain]

If you have been shooting at 1000 + yards in a no wind condition to test your true bullet drop for your drop charts, you should have seen the effects of spin drift and how it pushes your bullet on the target to the right. Not enough long range shooters do enough range testing in no wind and in wind conditions to see how all types of bullet drift and winds effect your bullet including more than one wind direction to your target and vertical winds. The ones that have put in the time and effort will see the big advantage they have over shooters that havn't.lightbulb

 

[Boss Hoss]

Well its good to see folks are beginning to wake up and smell the coffee. I got run off over at snipershide a couple of yrs. ago by the illustriuos( Frank ) for suggesting such a thing existed. I think even he now admits it exists but maintains it just isnt worth worrying about.

Most of the Idiot's over there read SOF and think they know everything there is to know LOL!! Truth is they are for the most part wanna be's who wear "tactical underwear" read sniper books and eat chili with their fingers while posting on the "hide"!! Always have a good time shooting against them in egg shoots----they just do not understand….

 

[Augustus]

When I first got interested in longrange shooting I did not do a lot of research and was overwhelmed by the hype surrounding the 50 cal generated by some of the manufacturers who were selling the round to the military. I bought an AR 50 and proceeded to shoot some of the military ammo from various countries. I quickly discovered that for precision longrange shooting the combo I had was just about useless. I then aquired the reloading equipment needed to produce my own ammo and began to see fairly decent results.

I was zeroing at 100 yds and was using a USO Horus Reticle for holdovers. I noticed my groups were drifting ever farther to the right as the distance increased. I went through the pain of installing a rail level and using a plumb bob at distance to get the level and my reticle tuned and verticle. Hmmmm, the rds still drifted right.

At this time I had never heard of spin drift but I was fairly sure my rds were drifting right and there was nothing I could do to stop it, it seemed to be about 1 min. I posted this on the HIDE and immediately was bombarded by folks that told me I needed to work on fundamentals. One told me he had discovered if he curled his little toe on his right foot the problem was fixed. Others told me I was not intelligent enough to tell if the wind was blowing or not. They just about had me convinced my problem was caused by the fact that I was born naked. I finally came to the realization I was experiencing about 1 min of rightward drift and it was very consistant so I might as well acccept the fact and compensate for it just as wind is compensated for.

I tried to figure out why there was such resistance to the idea of spin drift and here is what I believe. Most of the people who are the most vocal in debunking the idea of spindrift will be instructors who are in the business of teaching fundamentals of shooting. They will downplay the importance of equipment induced errors and are quick to blame the errors on a shooters technique. Just think how many schools one would attend trying to stop bullets from drifting to the right.

I was attending a school and one of the students was having a terrible time keeping his rounds under 2 min at all distances. He had a whole gang of instructors gathered around him telling him what he was doing wrong. I felt sorry for the poor guy and went to his position and told the instructors I thought I knew what the problem was and would they care to hear my ideas.

One of the instructors was a very nice man and said " Sure Im about out of ideas". At that point I set my pet .308 beside the shooter and piled up a few rds beside it. I laid down beside him and said "Here try this one for a spell". The shooters poor shooting skills suddenly dissappeared and he began hammering everything in sight. Dont get me wrong, shooters can induce a lot of errors into a system but all the fundamentals in the world will not make a bad rifle shoot good or circumvent the laws of the universe.

 

[RDM416]

Thanks guys for the responses. I guess the biggest lesson I learned here is that when you start playing at 1000 yards and beyond, there is no variable so small you can just ignore it. It all matters!!

 

[backwoods83]

I was told that this would happen when I went to my first 1k match, the guy that has been helping me for a while he said even though your dead nuts at 100yrds and the wind is calm your gonna hit low and 7-8" to the right, he went on to explain spin drift and cold bore shots, people used to think that spin drift didn't come into affect until after 1500yrds, way wrong. It gets even worse if you were to use for instance a 168grn vld in a 300wm with a 10 twist because then you really got it spun up, it'll drift way worse.

 

[cowboy]

Not enough long range shooters do enough range testing in no wind and in wind conditions to see how all types of bullet drift and winds effect your bullet including more than one wind direction to your target and vertical winds. The ones that have put in the time and effort will see the big advantage they have over shooters that havn't.lightbulb

Good advise and I couldn't agree more - however when you live in Montana - the only time I've ever seen NO WIND was about 5 minutes before the big one hit you and it's always 110F in the shade.

 

[bigngreen]

Good advise and I couldn't agree more - however when you live in Montana - the only time I've ever seen NO WIND was about 5 minutes before the big one hit you and it's always 110F in the shade.

Ya, I've been looking for a no wind day for a few years now, gave up!!!

The range I do most my shooting on has a prevailing wind that is left to right and I was convinced I sucked at calling the wind or my gear was crap until I started working on taking more into account. Taking all the variables into account I can has allowed me to work on getting better calls on the actual wind conditions I'm experiencing which translates into learning how to read actual conditions for a cold bore shot in a hunting situation of the range.