Left @ 300 yds - Right @ 1000 yds? WTH?

[4xforfun]

Phorwath,

I have not read all the posts here, but I wanted to tell you that I read an article on "Gyroscopic drift" which has nothing to do with the earth rotation, and this article said that the gyroscopic drift, on small arms ballistics, it is typical 8" to 9" drift to the right at 1000 yards for a right hand twist barrel. To that we add the coriolis efect and it looks like that might be your problem...

I believe that this is called the "magnus" effect. I thought about that last night. I knew I had just read about it not long ago....there it was...In the PS book on 1000 yard shooting....in the section on military sniping at 1000 yards+. I have taken my gun from 300 to 1000 and back forty times at minimum this year (I always dial back down to my 300 yard zero after a day om matches) and I don't ever remember being off by much....but, then again...I never shot 1 K in any windless days all summer, and had to always dial in some amount of windage. So, it could be!!!

Next chance I get I am going to shoot a windless day and shoot 100, 300, 600, and 1000 without dialing ANY wind....just to see.

 

[Pdvdh]

Re: Left @ 300 yds - Right @ 1000 yds?

Cool! But you don't need to shoot at four separate distances unless you're just shooting for the fun of it. If you shoot at either 100 or 300 yds and then on out to 1000 yds, you should see some gyroscopic drift if it's in play with your bullets. Spindrift is more pronounced the farther the ranges you're shooting. That's why I'm only shooting at two distances - one maximum range and one other relatively close distance. If I shoot 300 and 1000 yds, I should be able to see some gyroscopic drift if it's there to any appreciable extent. That is provided I've got my scopes installed plumb with the receiver and the rifle plumb with gravity and don't cant the rifle in either direction while touching off the shots. Let us know which caliber and bullet(s) you're shooting and what kind of results you come up with?

I'll be doing the same with my 300 Win Mag. I'm hoping I'm not shooting any major league curve balls. Maybe a tad bit of a slider, but hopefully no curve balls.

 

[4xforfun]

Re: Left @ 300 yds - Right @ 1000 yds?

cool! But you don't need to shoot at four separate distances unless you're just shooting for the fun of it. If you shoot at either 100 or 300 yds and then on out to 1000 yds, you should see some gyroscopic drift if it's in play with your bullets. Spindrift is more pronounced the farther the ranges you're shooting. That's why i'm only shooting at two distances - one maximum range and one other relatively close distance. If i shoot 300 and 1000 yds, i should be able to see some gyroscopic drift if it's there to any appreciable extent. That is provided i've got my scopes installed plumb with the receiver and the rifle plumb with gravity and don't cant the rifle in either direction while touching off the shots. Let us know which caliber and bullet(s) your shooting and what kind of results you come up with?

I'll be doing the same with my 300 win mag. I'm hoping i'm not shooting any major league curve balls. Maybe a tad of a slider, but hopefully no curve balls.

Just for the fun......and I have some loaded rounds that I need to "dispose" of.....I like to start fresh each year!!

 

[Eaglet]

I believe that this is called the "magnus" effect. I thought about that last night. I knew I had just read about it not long ago....there it was...In the PS book on 1000 yard shooting....in the section on military sniping at 1000 yards+. I have taken my gun from 300 to 1000 and back forty times at minimum this year (I always dial back down to my 300 yard zero after a day om matches) and I don't ever remember being off by much....but, then again...I never shot 1 K in any windless days all summer, and had to always dial in some amount of windage. So, it could be!!!

Next chance I get I am going to shoot a windless day and shoot 100, 300, 600, and 1000 without dialing ANY wind....just to see.

4xforfun,

I think the "Gyroscopic Drift" is different to the "Magnus Effect". The info. below was obtained from LoadBase 2.0 instruction manual:

 

[Pdvdh]

Re: Check out this LRH Thread

With respect to spindrift and determining it's affect with my two rifles, I've been reinventing the wheel. I just came across this LRH thread which covers the topic very well, and a lot of other information on proper scope mounting that I could have benefited from. If you're interested in this topic, this is a must-read thread:

http://www.longrangehunting.com/forums/f19/spin-drift-28008/index5.html

 

[Eaglet]

Re: Check out this LRH Thread

With respect to spindrift and determining it's affect with my two rifles, I've been reinventing the wheel. I just came across this LRH thread which covers the topic very well, and a lot of other information on proper scope mounting that I could have benefited from. If you're interested in this topic, this is a must read thread:

http://www.longrangehunting.com/forums/f19/spin-drift-28008/index5.html

Phorwath, thanks a bunch; I read all five pages, you're very right, it is a must!!!

 

[Pdvdh]

Re: My Spindrift Test Results

OK. For those that still have the interest...

I shot both rifles again in windless conditions, after getting the scopes mounted properly. My scopes are now mounted parallel with the barrelled receivers and with crosshairs perpendicular with the barrelled receiver. I've install bubble levels on both rifles to minimize any shooter induced canting of the rifles.

I first sighted both rifles dead on at 990 yds. I next shot both rifles at 300 yds and measured the distance the bullets were hitting to the left of poa.

My 300 Win Mag, 210 gr Berger VLD Match, ~2900 fps MV, 1-10 twist barrel - is hitting 3 1/2" left at 300 yds in order to hit dead on at 990 yds. These 210 VLD bullets hit approximately 1.11 moa left at 300 yds in order to hit directly on at 990 yds out of my rifle.

My 7mm Rem Mag, 168 gr Berger VLD Match, ~3070 fps MV, 1-9 1/4 twist barrel - is hitting 4" left at 300 yds in order to hit dead on at 990 yds. These 168 VLD bullets hit about 1.27 moa left at 300 yds in order to hit dead on at 990 yds out of my rifle.

From what I've read, 1/2 to 1 moa spindrift is typical at 1000 yds with these long, streamlined VLD bullets. Both bullets are drifting to the right more than 1 moa in my rifles. I don't know what's causing the additional left to right drift. But the majority of my drift is attributable to spindrift.

 

[Eaglet]

Phorwath,

Very cool info. Thanks for sharing.

It goes right along with what we've been reading!!!

 

[royinidaho]

phorwath'

The great think about your diligence is that now you know that you know!

Why? May be debated fro a long while. But nevertheless it there on those two rifles.

I'll be interested in your resolution.

Hold for it? Click for it, as in introduce a wind drive, which may mess up your 900 yd zero??

Or put golf ball dimples on one side of the bullet and slice/hook it a bit This may be difficult. If I remember correctly those Bergers are round which makes it difficult to determine which side to put the dimples.

 

[Boss Hoss]

This is one reason I use bored rings on all of my long range rifles and make sure that my Smith has the holes for the bases perfectly aligned prior to even mounting anything. . That is the way he builds his rifles for competition and I have never had a problem with any of the 15 rifles he has built for me.

If there is a problem after that then something else is amiss..

 

[royinidaho]

ah, the plot thickens.

My interest is way up on this one.

I'm stuck, so far, with factory actions. Hole alignment is probably debatable.

I've recently went to double dove tail bases and rings. That 'should' help a bit????

How would some one such as myself, professor though I may be, check the scope alignment?

A 1" or 30 mm rod the length of the action and barrel?
A "sun shade" 30" long?

Then observe the differences at the muzzle?

How about centering the reticle, or very close to it, then do the laser cartridge bore sighter thing observe the difference between the vertical and the dot?

Or send the action to a good smith and rebore the mounting holes to the next size up while simultaneously correcting any alighment issues?


Boss Hoss, just shows ya how much of a professor I really am.

 

[Boss Hoss]

Ahhheeeemmmm---the Professor is not feeling well and will be back to the lectern later this afternoon with the answers! For now---RECESS!!!!!


Roy to tell you the truth Speedy does it on my rifles during the build process---do know that sometimes we use a larger screw size to hold the bases when the holes are not perfect. Have not had to relocate any on Jerry's stuff and that includes all of my Predator's so far. Just picked up my latest stick on Saturday 6.5 WSM on a Predator using John Loh "Speedy" rings and Davidson bases. John's rings are from "Super Alloy" 7050 T-7 which is the best material for non steel rings that exist IMHO. Just got 3 sets last week and have the old 7075 in a T6 condition on many other rifles. When all of the pre fitting is done the scope fits like it was poured into the rings which is the way it should be(very little lapping if any will be required).



HEY YOU BOY-----GET AWAY FROM THOSE CURTAINS----PAY NO ATTENTION TO THAT MAN BEHIND THERE!!!!!!!!!!!!!!!!

 

[Michael Eichele]

This really is alot simpler than it seems. Mathematically (and in the real world) you shouldnt have more than 6" of right hand drift at 1K in standard air density with either cartridge and load. Any FURTHER right hand impact is one of 2 things. Unknown wind or a canted rifle (due to scope misalignment) or both. Since it seems you are very sure the has been no wind and the results are always the same I would step out on a limb and say it is your scope alignment as has already been mentioned.

For those that dont believe in spin drift and all the naysayers, you cannot defy physics. It is real and is NOT voodoo. ALL rifle and bullet combinations WILL yeild to at leat some spin drift. If your experiances show otherwise it is nothing more than a scope that is ever so slightly misaligned (usually accidentialy) to YOUR benefit.

Personaly I set up my scopes in the smae manner. That is slightly misaligned to offset the effects of it so I dont have to adjust my windage knob for it. Believe me, it doesnt take much offset to counter it.

 

[Pdvdh]

meichele,

Where have you read about spindrift limitations of 6" at 1000 yds? I'm curious since I've read over on the sniper's hide forum where 10" and even slightly more spindrift isn't uncommon with some bullets at 1000 yds. The thread on Sniper's Hide was posted somewhere earlier in this thread and it's a very long thread and read. In summary, one of the guys posting was somewhat of a military-experienced expert on the subject, and he's the source of my information on 1 moa (~10") or more spindrift possible at 1000 yds. 10" is 67% more than 6" spindrift, so I'm looking for closer agreement/consensus on potential magnitudes of spindrift at 1000 yds.

I did indeed have my scope mounted crooked on my 7mm Rem Mag and that's why I was initially seeing so much left to right drift. I'm confident I've got everything pretty well mounted straight with the world at this point. The excess left to right drift (above and beyond that attributed to spindrift) could still be due to slight misalignment of the scope on the receiver - so slight that I can't eyeball it. I'm not going to mess with my setups anymore at this point. Now that I've confirmed and quantified my left-to-right drift, I can make provision for it. If I was shooting at prairie dogs, I'd probably refine my setups further, but hits on big-game sized animals shouldn't be compromised due to my bullet drift now - out to at least 1100 yds.

My tentative plan is to leave the rifle hitting on poa at 1000 yds and allow the leftward hits at the closer, mid-ranges. I will shoot both rifles at the 600 - 700 yd range to confirm my POI's and then see if I have more or less leftward POI than I'm currently getting at 300 yds. I can live with 4 inches left at the intermediate ranges. I'd rather be 4 inches left at midrange than 10" or more right at 1100 yds. My rifles both peter out velocity and energy-wise by ~1100 yds.