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On Paper Vs Ballistic Program

 
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  #1  
Old 08-29-2007, 10:46 AM
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Location: El Campo, Tx
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On Paper Vs Ballistic Program

I realize numbers in the computer and bullet holes on paper can be way off. Kinda like theory and reality. I am shooting a Remington sendero 300 rum 6.5 x 20 long range Leupold with a gentry brake. I am loading 100.5gr retumbo w/ 180 gr accubond. I have chronographed the load at 3355fps avg. I am shooting 2.8 inches high at 100 for a 300 yard zero. Here is the problem, when I shoot the 300 yd target, I am actually 3.5 in low. My question is how do I dial up to 400 yards or further if the ballistics info is that inaccurate at close range.
I am using the shooting chrony's ballistic program. Any suggestions other than shooting and documenting the poi. at all ranges? I am limited to a 300 yard shooting range. I am new to trying to strech the range but not to shooting out past 300 yad. I just have never had the optics or a flat shooting rifle to do so.
Thanks for the responses,

Shawn
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  #2  
Old 08-29-2007, 02:09 PM
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Location: Chelan Co, Washington
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Okay - old school solution here - I have messed around with some of the programs, and some are okay, while others seem to be very error prone. That said, I'm pretty much old-school on this one.

Feel free to disagree, but if you want to hunt game at long range, I believe you should practice at long range.

There's a whole lot more to shooting at long range than dialing in the appropriate number of "clicks" and squeezing off a round. This little thing called "wind" comes to mind, and yes, even with a rip-snorting 3300 fps .300 Rem Ultra Mag, wind plays a major role - particularly at longer ranges. Most places I've hunted out west here have some pretty significant wind on a routine basis.

So - don't limit yourself to that 300 yard range. That may be all that's convenient, but a guy can get himself somewhere to shoot some range... If a real live 600 or 1000 yard rifle range isn't handy, and I realize they're scarce in places, there are alternatives. I've set up on public land. Along power lines. With permission on private property. All kinds of ways to get 400, 500, 600+ yards.

Having been surprised a few times when real-world trajectory didn't match what ballistics tables or programs told me... Well, I'm a firm believer in actually shooting your hunting rifle to the ranges you expect to use it at in the field.

Yeah - I know - I'm an old school stick in the mud about this stuff, but I generally hit pretty darned close to where I aim. Best of luck to ya.

Regards, Guy
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Old 08-29-2007, 02:26 PM
rdc rdc is offline
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I am by no means an expert at long range anything. But, do you think the published BC is too good to be true? That would put you low. I think that would be the case as most BCs don't even tell you which drag table they are correcting for ie: G1, G7, Ingals, etc.

I think shooting and chronographing at long range will give you the correction factor (BC or whatever) that might get you close.

But I agree, shoot at range. I always wondered why I missed reading the wind in high power. The charts I had were off and the click values in the data books were also wrong.

Okay, experts, do you use two chronos or just move the one to different ranges and get 10 shot averages to calculate the drag?
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Old 08-29-2007, 02:38 PM
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I agree with the old school basics. I have decided to check the BC on the load and check several other entries on the program but when it comes down to it, I am going to physically zero at 300 then shoot at 100 then 200 to see whats going on. I guess I will need to find a location where I can shoot at 4-500 yad just to see what the drop is to at least know what the hold over is. I am actually working on this rifle for a Colorado hunt in Nov. I shoot between 200-325 yad on average for mule deer but where the elk graze are between 4-450 yds. So I am hoping to get this thing sewed up before I long.
Thanks for the replies.
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  #5  
Old 08-29-2007, 02:52 PM
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I echo what Guy is saying about practice but I understand wanting to know a starting point. I have found that the ballistic calculator that I use is usually pretty accurate but not perfect. When I punch in the info you provided, I get a similar trajectory to what you expected. My calculator takes into account many variables that I had to guess such as elevation, temperature, and scope height. I used my own typical number of 1000 ft. and 70 degrees with a scope height of 1.5 (low mount). I used the more conservative number from Nosler's website of 0.474 for the BC. For this set of parameters and a 300 yard zero, the 100 yard impact should be plus 2.7 inches. A better way to get started is to zero your rifle at the intended zero range and work from there. I would click up 5 clicks and double check the zero and then shoot at the other ranges. I can't explain why the actual is so different from the calculator. Just playing with other parameters to match what you observe would take some drastic changes to the velocity or BC. A velocity of 2950 and a 250 yard zero would be close. A lower BC would require a value of half or less which cannot be the case. It could be combination of things. Anyway, it is critical that you shoot a group at each range to get accurate data. Don't just shoot twice and say that it's 3.5 inches low. A MOA rifle's group at 300 yards is going to be around 3 inches. Good Luck
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  #6  
Old 08-30-2007, 03:18 PM
rdc rdc is offline
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With your data, 350 yards shows -3.5 for a 300 yard zero. Are you sure the target is at 300 yards? Could it be 300 meters? Just a thought. I may get it wrong, but I keep thinking about it.
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  #7  
Old 08-30-2007, 03:35 PM
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what you need to do is shoot at 3 known distances other than the one your zeroed at and measure your drops, then you can either tweak the BC in you computer program till the drops are correct or use a program that allows to to "figure BC from trajectory". Published BC is never dead on everywhere, you need your actual BC and then use that number in your chart, just keep all the info as accurate as you can while figuring the BC.
RR
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