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I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

 
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  #1  
Old 08-18-2005, 07:27 PM
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I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

I was doing some testing resently. Here is the scenario:

Custom 300 RUM (.333 ND) 27.25" Lilja #7 straight taper, 12 twist with a muzzle brake. Night Force NXS NP-R2 3.5-15x50mm. 95.0 H50 BMG 178 AMAX at 3100 on the nose. 300 yard zero. Dead nut zero I might add. A reliable chrony was used to determine 3100 FPS. This load was also chronographed during multiple sessions on different days. When I went to test this load at 600 yards something interesting happened. The bullet drop at 600 yards was only 37.7" The conditions at the time were 29.61" hg. 26 degrees F. 88' 77% humidity.

Now the published BC for the 178 AMAX is .495 or .496. Most shooters here will agree that on the G1 curve out to 600 yards the BC is more like .515 to .525. Using .525 I have to enter 3440 FPS into the calculator to see 37.7" at 600 yards. If I use 3100 FPS the BC has to be 1.050 to make 37.7"

The method for determining drop was this:

NP-R2 = 2 MOA per hold over. 3 hold overs were used to hit dead nuts at 600 yards. 2 MOA = 2.094" * 3 bars = 6.282 * (600/100) = 37.692"

Real world bullet drop should be closer to 49"

I can see being a few inches or .05 in the BC, but these numbers are outragous.

Any ideas???

I forgot to mention that the hold overs in the reticle have been proven to be an actual 2 MOA
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Old 08-18-2005, 08:24 PM
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

Are the stadia a constant 2 mils at ALL magnifications? Or is it only 2 mils at a specified setting?


Subtension on many scopes changes with the power setting.
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Old 08-18-2005, 09:29 PM
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

I have no explaination for you accept that I share the same amazing performance. I shoot a host of Hornady SST and Amax bullets in various cals. Velocities verified with chronies, scope adjustments verified at 100yds on graph paper.

My 6.5 140gr SST flies stupidly flat and have had some superb results with the 165gr 30cal SST. The 30cal 155gr Amax fly way flatter then any other HP match bullet of equivalent of heavier weight from my 308.

Just started playing with the new gen 162gr Amax and 150gr SST in 270. The 270 shows more normal come ups but the 162gr 7mm Amax is looking pretty flat. got some old gen 162gr Amax and these are even longer and look much more aero.

Historically, the 6.5 140gr Amax had a very high printed BC number and probably flew better then that. Then they redesigned it to make it way less aero. Now the SST has that old shape and again flies really well. I wonder if the 6.5 Amax will be changed to its former glory?

I just go with the flow and figure that something in my gear or measuring is off. But then again, could just be magic...these poly tipped bullets fly well.

Now the Interbonds are even longer for their bullet weight.

Jerry
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Old 08-18-2005, 11:46 PM
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

That is a very good point BB. Yes, my hold over values will change with power. The tests were done on 15x, which is where my reticle = 2 MOA per hold over.

Jerry, I am glad someone else shares this phenomenon. I have run the numbers every which way and just cant figure out why it shoots soooooo flat. 10" at 1000 isnt much, but 10-12" at 600 yards....Thats a HUGE differance. Oh well, I will just take my rediculously flat shooting load and be happy with that. (Its my sheep load)

The funny thing is that when I shoot 155 AMAX's out of the same rifle at 3600 FPS, they fall at 600 yards VERY close to what the calculator sais they should based on a BC of .474, which is what it was in the real world in my 308. The 178's however WAY out perform the 155 AMAX.

Thanks guys
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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Old 08-19-2005, 02:09 AM
daveosok
 
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

Try using the G7 from JBM's web site .
I entered all your data except Altitude which you did not state and my drop came up with 37.7 @ 600 yards dead on the nose.
This was using your 300 yard zero and the BC of .495. The G1 function is a broad general usage function. The Amax is completely different and requires a different G function.
<font class="small">Code:</font><hr /><pre>Range Velocity Energy Momentum Drop Windage Lead Time
(yards) (ft/sec) (ft-lbs) (lbs-sec) (inches) (inches) (inches) (sec)
0 3103.1 4703.7 3.03 -1.5 -0.0 0.0 0.000
100 3010.4 4426.8 2.94 2.9 0.0 0.0 0.098
200 2918.9 4161.9 2.85 3.5 0.0 0.0 0.199
300 2828.8 3908.7 2.76 -0.0 0.0 0.0 0.304
400 2739.9 3667.1 2.68 -7.8 0.0 0.0 0.412
500 2652.6 3436.9 2.59 -20.3 0.0 0.0 0.523
600 2566.6 3217.9 2.51 -37.7 0.0 0.0 0.638
700 2482.2 3009.7 2.43 -60.4 0.0 0.0 0.757
800 2399.4 2812.1 2.34 -88.8 0.0 0.0 0.880
900 2318.1 2624.9 2.26 -123.1 0.0 0.0 1.007
1000 2238.5 2447.7 2.19 -164.0 0.0 0.0 1.139 </pre><hr />
My MOA chart says
<font class="small">Code:</font><hr /><pre>______________________Yards_________________ _______
_______100____200____300____400____500____600
MOA __1 MOA 1.04 2.094 3.141 4.188 5.235 6.282
____2 MOA 2.094 4.188 6.282 8.376 10.47 12.564
</pre><hr />
You have three moa lines but multiplied it by 2.094 instead of the moa valua of 2 moa at 600 yards which would be 3*12.564 or 37.692 is what is actually being covered in distance at 600 yards. Which is dang close to the drop I got using the JBM calcualtor on a G7 function.
I hope this helps you out some.
You got it right but went about it a different way than I did [ QUOTE ]
NP-R2 = 2 MOA per hold over. 3 hold overs were used to hit dead nuts at 600 yards. 2 MOA = 2.094" * 3 bars = 6.282 * (600/100) = 37.692"


[/ QUOTE ]
Dave
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  #6  
Old 08-19-2005, 06:14 AM
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

Dave, I'm assuming you know how to properly choose the G# for a given bullet. Can you explain what this is and how you determine which one to use? I'm not really familiar with it, but I'm guessing it has to do something with how the BC changes over the course of flight, similar to how Sierra publishes their data.
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Old 08-19-2005, 08:06 AM
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Re: I am SOOOOOO confused. HEEEEEEEELP!!!!!!!!!!!!!!!!!!!!!!

I hadnt tried the G7 curve, but I can see that when the G7 curve is used, its MUCH closer.

I didnt think that at 600 yards the differance between G1, G5, and G7 would be that differant. I even have 2 personal calculators that utilize the G7 curve. Thankx for pionting that out. I learn something every day!! [img]/ubbthreads/images/graemlins/laugh.gif[/img]
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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