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MilDot Calculations and zoom

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  #15  
Unread 06-08-2009, 06:39 AM
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Join Date: Apr 2009
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Re: MilDot Calculations and zoom

As much as you want to be old school.....and I think that's cool. You might want to consider an electronic range finder for verifying you mildot calculations......it's quicker than driving to the target and probably a bit more accurate. Even if you still choose not to use it before hand. IMO they are the best thing since sliced bread. While using the Long Range Simulator, if I "cheat" and know the yardage ahead of time....as long as I calculate the wind correctly I'm guaranteed a first shot hit every time.
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  #16  
Unread 06-08-2009, 07:42 AM
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Re: MilDot Calculations and zoom

Another voice of wisdom comes to light.

I have tried to access the site you gave me the link to, but cannot access it at all.
Would you be referring to the formula : Target height (yards) divided by Target height (Milradians) multiplied by 1000. The answer is your range in yards.

Actually, the amount of information you people are collectively throwing at me is quite mind boggling ! A bloke should stop shooting for a month and start trying to digest it all - fascinating stuff !

Thanks,
Pete.
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  #17  
Unread 06-08-2009, 07:59 AM
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Join Date: Jul 2008
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Re: MilDot Calculations and zoom

Well now my friend back from the Netherlands, give me some time to go and do some further reading, then you may have a better quality discussion.

Actually, I only have another 400 yards (100 yard increments) to finish ranging this scope in and all will be well.(Hopefully !) I reckon my capabilities would not go much beyond 1000 yards. Maybe that will change when I manage to purchase a really good quality scope.
I have to drive back to the target, by the way, not only to see how far it is, but also to see if I have hit the damn thing !!!!!
Thought that may offer some amusement by the way.

Will continue this later,
Cheers,
Pete.
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  #18  
Unread 06-09-2009, 05:57 AM
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Join Date: Jul 2008
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Re: MilDot Calculations and zoom

I was just mulling over this thread today and picked up on something SSCOYOTE mentioned. Dial up scope turret for bullet drop, but use MilDot to hold off on wind. It has just occurred to me I do the same.
I seem to work out the wind much, much better than holding over using the Dots for bullet drop - my brain must be wired differently I think.
This brings me to the question:
What sort of effect does a head or tail wind have on a projectile?
Cheers,
Pete
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  #19  
Unread 06-09-2009, 09:49 AM
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Join Date: Jun 2009
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Re: MilDot Calculations and zoom

Head and tail wind are insignificant in most drop compensation. To bring it into perspective, the change in velocity through the mass of air is generally less than the velocity spread of your ammunition. (15mph=22fps). Even with a ~20fps difference in bullet velocity, vertical stringing is pretty small out to 1000yds, probably considerably smaller than most will be able to shoot given skill and equipment. Unless you have a real laser of a rifle and the ability to stack bullets at 1000yds in world record size groups, you will probably be chasing a unicorn trying to adjust for head/tail wind. But if you must, bullet impact will be lower in a head wind and the converse is true for a tail wind.
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  #20  
Unread 06-09-2009, 10:55 AM
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Join Date: Oct 2007
Location: Patagonia Mountains, Arizona
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Re: MilDot Calculations and zoom

Quote:
Originally Posted by peterb View Post
What sort of effect does a head or tail wind have on a projectile?
Cheers, Pete
In Chapter 7 of Robert McCoy's book "Modern Exterior Ballistics" the math is given to calculate the effect of head and tail wind. He gives the example of an M2 ball bullet (30-06 @ 2800 fps) with a 10 mph tail wind and demonstrates that causes the point of impact at 600 yards to be raised by 0.7 inches relative to not having a tail wind.

Basicly a tail wind decreases the time of flight by slightly reducing the drag on the bullet. That affects the drop simply from reducing the time the acceleration of bravity (32 ft/sec^2) is applied to the bullet before impact. A head wind likewise increases the time of flight lowering the point of impact.

Many ballistic computer programs are based on McCoy's work and include the effect of the head and tail wind components in the calculations. You can check if your's does by including a head or tail wind in the calculation (if the software has a place to enter a 0 or 180 degree wind) and see if it causes the expected small change in the calculated drop. You can then check the effect on your particular bullet/velocity/atmosphere at various ranges. Drop however is related to the square of the time of flight while croswind effects are linear with the time of flight.

Head and tail wind effects are generally much smaller than crosswind effects at practical ranges but do increase with range more than crosswind effects. If you're worried about it let your ballistic computer show you the effects.
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  #21  
Unread 06-09-2009, 05:08 PM
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Re: MilDot Calculations and zoom

Thanks for that gentlemen. I have never been lucky enough to hit the wind square on, but it has always been one of those "I wonder what if ............. "
Obviously, with a tail wind, there is not much to shoot 'cos it has usually bolted anyway !

Cheers,
Pete.
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