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my drop chart doesn`t match at 500yds and beyond?

 
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  #8  
Old 06-14-2001, 02:10 AM
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Join Date: Jun 2001
Location: Palmer, Alaska
Posts: 2,539
Re: my drop chart doesn`t match at 500yds and beyond?

Thanks for the time and help everyone. I`ll try to fill in the blanks and clarify some choppy statements, tried to be brief, sorry for the confussion.

Temp +69 deg F
Alt. approx. 150' above sea
horizontal
wind 10-20 at 11 o`clock (12 being muzzle end)
1 in 14 twist

I`m useing two different Crony brand cronys at 15', and both read between 2525 and 2610 with variances as much as that between them on the same shot. And top of that one will be faster one time and the other the next.
I think these are ball-park brand cronys, wish I had bought a good Oehler model.

Bullets print perfect holes at all ranges in paper and plywood backer with no evidence of elongation and if I remember correctly the programs indicatd quite a slow twist rate of between 19 and 21 depending on muzzle vel.

The first moa chart is exactly the mark set at on the leopold dial that my bullets hit dead center for each distance indicated. The second chart below that is the exact moa the two programs I use come up with, based on 2550 fps with a .546 BC.

But the main reason I used this chart at this vel. and BC is not just that my crony said 2550 but I feel more importantly that the moa adjustments for the first 400yds matched exactly those of mine.

I was unable to duplicate this 400yd path with any manipulation to MV or BC. It seems no mater what I do to MV or BC or combination of both on the program, if it matches perfectly to 400yds it is always flatter at 500 and beyond than my groups print.

What I ment to say on the 800yd group was, when I shot my 800yd groups dialed in at the 31.75 I suspected I needed the group printed 15" low and 10" group. So on the program if I entered in 2400 MV thinking my crony is lying to me, I find that would be more like it.

Only one problem, that chart indicates my bullet should not be flying as flat as it apparently is by far at up to 400yds if it were going that slow. It would be printing several inches lower at my setting of 2.25, 5.25 and 9.00.

The main reason I try to find a drop chart on the program matched to my known drops to 400yds is just to establish a path my bullet is following for the further distances to keep them on the paper.

One more observation I`ve made correctly I hope is that if my scope is not calibrated for true moa and just 1" at 100yds instead, I would indeed be needing more clicks at the greater distances to make up for this especially if it is slightly under an inch.

What is the most exact way to measure this in your experiance?

I checked out the chart with a BC .450 and it seemed to be real close at 700yds but seems 800yds is SEVERAL inches off still.
I`ll go to the range again and check a few things out. I was going to go back to 900 and 1000yds but looks like my scope has about 34.75 moa maxed out with a .025" shim already under the rear base.

I wonder if like you say Warren, the bullet might be "overspun" and BC is falling off at distance as a result. What you say Darryl about matching the program to the product hit the nail right on the head. Thanks again for the quick response with all the help and suggestions.
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Brent Moffitt
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  #9  
Old 06-14-2001, 03:48 AM
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Re: my drop chart doesn`t match at 500yds and beyond?

I e-mailed Leupold tech service a while back about the internal adjustments on thier scopes. The reply was that ALL thier scopes are true MOA adjustment. (I post this not because I automatically believe them but because it's what they state.)
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Old 06-14-2001, 06:10 AM
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Join Date: May 2001
Location: Arco, ID 83213
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Re: my drop chart doesn`t match at 500yds and beyond?

Brent,

Yes, based upon your observations you do have BC decay, but you now know where your bullets will print at the various ranges. You can work with that.
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  #11  
Old 06-14-2001, 09:16 PM
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Location: Palmer, Alaska
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Re: my drop chart doesn`t match at 500yds and beyond?

My own charts will work just fine. Something Ken H. asked on another thread was how accurate are these Bushnell rangefinders? Well thats a possibility, my YP1000 may NOT be as accurate as as I thought.

It sure is repeatable and my range is set up based on the rangefinder, what I use in the field, not a tape, etc. If calibration is off just 2,3 or 4 yds every 100yds, multiply that out at 500+ yds and it is a real problem with trying to match it to charts for true yardage. I`ll let you know what I find when I measure things out.
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  #12  
Old 06-20-2001, 02:57 PM
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Join Date: May 2001
Location: Stevensville, Montana
Posts: 14
Re: my drop chart doesn`t match at 500yds and beyond?

FWTW, a couple of echoes and cobwebs from the void in my gourd. If you were here, we could run some loads through the acoustic target and get a better grip on the de facto, field-derived BC. (I've heard industry people, asked how they get their BCs, say "We figure 'em as close as we can, then we look at what the competition claims." That has always filled me with about as much confidence in their figures as there's nourishment inside a ping-pong ball.)

Also, the equations in your software may be the usual, traditional equations that have worked so well, for so long, because we small-arms riflemen never put 'em to the strain that your shooting puts on 'em. I asked the late Homer Powley what value there was in Art Pejsa's equations, and he said that the Pejsa equations are minutely more accurate than the traditional. I've heard users say that Pejsa's equations are noticeably more accurate out to 1,000 to 1,200 yards. I don't know anyone who's tested 'em farther out than that.

I may have just wasted your time. I haven't checked any of this out, so I'm just throwing somebody else's cats into the burgoo. Strain the hair out for yourself. Hope I didn't ruin the pot.
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