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View Poll Results: Do you use a scope level to keep your rifle level?
Yes, of course! 926 45.15%
No, I don't shoot over 300 yards. 238 11.60%
No, but I really should use one. 887 43.25%
Voters: 2051. You may not vote on this poll

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Do you use a scope level to keep your rifle level?

 
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  #71  
Old 11-22-2011, 10:39 PM
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Re: Do you use a scope level to keep your rifle level?

Quote:
Originally Posted by Eaglet View Post
Gotta have it!
Agreed.
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  #72  
Old 11-23-2011, 05:56 PM
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Join Date: Jan 2009
Location: Mich.
Posts: 76
Re: Do you use a scope level to keep your rifle level?

I don't shoot too much out past 300 yds. but I do use this level to mount all my scopes.. It is made to leave on your Rifle if you want to keep it level, mounts to the base, It is hard to hold a Rifle perfectly level while shooting, I can see how this would be a big plus in long range shooting..
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  #73  
Old 11-26-2011, 10:41 AM
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Join Date: Oct 2007
Location: Patagonia Mountains, Arizona
Posts: 753
Re: Do you use a scope level to keep your rifle level?

Maybe this diagram will help explain the effect of rifle cant and how to calculate the effect. The drawing isn't ideal because no one would cant their rifle as far as even the first angle shown, but I think it can explain why it's important even for small angles.


In this diagram red dot marked 1 is both the point of aim of the sights on the rifle and the target (point of bullet impact without cant) . The red dot 2 represents the point above the target where the bore is pointed. The vertical linear distance between dot 2 and dot 1 is the total drop of the bullet at the target, in inches for this example,, not in MOA or Mils. The green dot 3 is where the bore will be pointed (in the plane of the target) if the rifle is canted (rotated about the target (dot 1) . In this picture the angle is 22.5 degrees (1/4 of 90) which is rediculously large, but it will do for example. Green dot 4 is where the bullet will impact in the plane of the target with the rifle canted.

Assume the target is 1000 yards, the rifle is a 300 Win Mag, the bullet is a 190 Sierra Match King. I'll use 5 degrees for the cant angle. That would be hard to sense in windy mountain terrain with no external physical clues as to where vertical is. A ballistics program shows that the total vertical drop at the target Dot 2 to dot 1 on the drawing from the combined effect of gravity and atmospheric drag will be 327 inches (2950 fps mv @ sea level)
The sine of 5 degrees is 0.087 times 327 = 28.5 inches. for the horizontal error. The distance horizontally from dot 1 to dot 4 at the target.
The vertical error will be (1-cos( 5)) * 327 = 1.24 inches. The distance vertically from dot 1 to dot 4 at the target.

For practical ranges and small can't angles you can ignore the vertical component of cant, but the horizontal component is quite significant and cannot be ignored for long range shooting. Even a 1 degree cant error will be a 5 to 6 inch error at 1000 yards for typical hunting rifles. Actually cant error can be accurately calculated only from bullet time of flight and the cant angle without any other information about the rifle or bullet since drop in inches is always 192xT^2 where T is the time of flight in seconds.

Why can long range benchrest shooters get away without considering cant? Because they are shooting groups and use sighters to null out the effect of cant and the benchrests insure that the cant doesn't change between shots. Those are both luxuries hunters usually don't have. Most do level the benchrests and square up the rifles and the rests even if the rifle it'self doesn't have a level affixed.

The sine and 1-cosine calculation only apply to small angles and aren't exact. The sight displacement from the bore isn't in the calculation nor is uphill/downhill shooting considered. . The purpose of this exercise isn't to calculate the effect of cant int the field. It's to show why having a level on the rifle is worthwhile for LongRangeHunting.

Last edited by LouBoyd; 11-26-2011 at 11:14 AM.
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  #74  
Old 11-26-2011, 11:07 AM
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Re: Do you use a scope level to keep your rifle level?

Louboyd,

Great explanation. The question that I have is that if you have your site level mounted but your horizontal cross hair isn't exactly parallel with the bolt rails, could you still get consistent accuracy at all ranges as long as you are using the scope level for all shots? Thanks.
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  #75  
Old 11-26-2011, 11:53 AM
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Join Date: Oct 2007
Location: Patagonia Mountains, Arizona
Posts: 753
Re: Do you use a scope level to keep your rifle level?

Quote:
Originally Posted by Greyfox View Post
Louboyd,

Great explanation. The question that I have is that if you have your site level mounted but your horizontal cross hair isn't exactly parallel with the bolt rails, could you still get consistent accuracy at all ranges as long as you are using the scope level for all shots? Thanks.
You can't get "consistent accuracy" even if everything is square and level. Bullets don't fly in a vertical only plane. Consider spin drift, wind deflection, etc.
If a rifle has a built in cant angle it will still shoot small groups as long as that angle is not changed. However, if you want to make first shot long range hits by using ballistic calculations you have to account for all of the things which determine where the bullet will impact both with respect to the scope and the rifles bore and the flexure of the rifle and the subtleties of how spinning projectiles behave in the atmosphere. You can try to calculate all of those things but it's very difficult. In my opinion the best results come from aligning everything as best you can keeping in mind the magnitude of each of the errors. Then actually shoot the rifle and measure where the bullets go. They should be close to calculated but will never be exact. For one thng G1 and G7 ballistic tables are rarely exact for small caliber bullets. Use the measured differences vs distance to modify calculations either with range cards or offsets for ballistic calculators. The objective is to be able to predict how to aim your rifle to get correct first shot impacts based on current conditions as best you can measure the conditions. Cant is an error source which can be eliminated with a simple level, just as range can be measured precisely with a laser rangefinder and slope with an inclinometer. Air density is a simple measurement.

What's left? Wind is relatively simple to measure at the shooters location but it can change rapidly and wind over the rest of the trajectory can be more important for long range shooting, particularly when it's not uniform versus distance which it rarely is. Downrange wind conditions are the major variable that few people can estimate well and I know of no portable equipment which can give reliable downrange wind information. The use of sighter shots measures the effect of many variables simultaneously but it's often not practical when hunting.

Doping wind is a skill that has to be learned through practice in field conditions, but that's a subject for other discussions.
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  #76  
Old 02-27-2012, 03:04 PM
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Join Date: Nov 2011
Posts: 397
Re: Do you use a scope level to keep your rifle level?

You bet I do. I learned this bit of info many years ago. When archers started hanging sights on our bows. A slight cant and your off target. Also helps with hill side shots, cant the bow or rifle into the hillside depending on how steep the hillside is. The steeper the more cant. Watch the bubble and you will soon find out how much bubble to use.

If you don't think it works try it. Only cost you a bullet or two. Just another piece of your sighting mechanism.

I would like to see some scope manufacturer incorporate a level into the bottom of the retical.
Archery sight makers have been doing it for years.
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  #77  
Old 02-27-2012, 03:54 PM
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Join Date: May 2009
Location: Prosperity, Pa
Posts: 373
Re: Do you use a scope level to keep your rifle level?

"I would like to see some scope manufacturer incorporate a level into the bottom of the retical'

Coming soon to Huskemaw!
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Last edited by paphil; 02-27-2012 at 03:55 PM. Reason: spelling
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