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Trouble Matching bullet drop

 
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  #1  
Old 10-18-2010, 01:58 AM
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Join Date: Dec 2008
Posts: 27
Trouble Matching bullet drop

G'day,

Have been having trouble for weeks and weeks matching my 600m (660yards), 900m (1000yards), and 1000m (1100yards) bullet drops with the ballistics programs.

The load is 60.5gn 2213SC pushing a 180gn Berger at 2820fps.

When dialled in at 600m my shots at 1000m would be 4-5 clicks flatter than what any program said. Vice versa when dialled in at 1000m it would be out by 4-5 clicks at 600m.

Was tearing my hair out trying to manipulate velocity an/or BC to get it to fit. No luck.

This weekend just gone shot a five shot group at 1000m measuring 10.5 inches wide by 4.5 inches height. Was wrapped with the rifle but still didn't match up at 600m.

Then I tried something different. I changed the clicks on the program from 0.1 mRad (scope a Nightforce 5.5-22x56 MLR metric) to 0.104mRad and suddenly 600m, 900m, and 1000m results matched the bullet's path.

Has anyone had any experience with some scopes being not quite true to their click values?

Or has anyone used the method of changing the click value in Exbal, JBM, or BulletFlight to make the trajectory fit the scope?

Any advice would be greatly appreciated.

Cheers,

Matt
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  #2  
Old 10-18-2010, 11:53 AM
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Join Date: Jul 2004
Location: Texas
Posts: 5,624
Re: Trouble Matching bullet drop

Quote:
Originally Posted by curiousaussie View Post
G'day,

Have been having trouble for weeks and weeks matching my 600m (660yards), 900m (1000yards), and 1000m (1100yards) bullet drops with the ballistics programs.

The load is 60.5gn 2213SC pushing a 180gn Berger at 2820fps.

When dialled in at 600m my shots at 1000m would be 4-5 clicks flatter than what any program said. Vice versa when dialled in at 1000m it would be out by 4-5 clicks at 600m.

Was tearing my hair out trying to manipulate velocity an/or BC to get it to fit. No luck.

This weekend just gone shot a five shot group at 1000m measuring 10.5 inches wide by 4.5 inches height. Was wrapped with the rifle but still didn't match up at 600m.

Then I tried something different. I changed the clicks on the program from 0.1 mRad (scope a Nightforce 5.5-22x56 MLR metric) to 0.104mRad and suddenly 600m, 900m, and 1000m results matched the bullet's path.

Has anyone had any experience with some scopes being not quite true to their click values?

Or has anyone used the method of changing the click value in Exbal, JBM, or BulletFlight to make the trajectory fit the scope?

Any advice would be greatly appreciated.

Cheers,

Matt
Matt.
The G7 Ballistic coefiecent of the Berger is a closer match than the G1 so try using the G7 and
the drops will be closer to the real thing.

Also scopes do have a little error from MOA to inches and if they are near the limit of their
turret travel there is more error because of thread clearance.

J E CUSTOM
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  #3  
Old 10-18-2010, 06:20 PM
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Join Date: Nov 2007
Location: Northern California
Posts: 16
Re: Trouble Matching bullet drop

If you make a grid graduated in MOA and look at it through a solid mounted scope at 105 yds, then click up through one or two turret revolutions you will likely get a big surprise. .25 MOA clicks are often not. I've seen them from .25 to .3 and everything in between. Not at all important if you know this but does confuse someone who hasn't observed it before. Also makes a significant difference at long range which you quickly realize once you've done the math.
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  #4  
Old 10-18-2010, 07:05 PM
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Join Date: Dec 2008
Posts: 27
Re: Trouble Matching bullet drop

JE,

Tried all various combinations of G1, G7, and Litz BC's to no avail.

Scope has 20 MOA base so should be in the middle of its travel.

rb,

I think my scope is one of those i.e. it moves 1.04 cm per click rather than 1.00 cm, because once I changed the ballistics programs to 0.104mRad values then 600m, 900m, and 1000m come up all fit the actual bullet trajectory.

Thanks,

Matt
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  #5  
Old 10-18-2010, 09:53 PM
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Join Date: Jan 2003
Location: North Louisiana
Posts: 643
Re: Trouble Matching bullet drop

Gadjets!!
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