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Drop chart ?

 
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  #1  
Old 02-14-2008, 10:47 AM
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Location: Queen Creek / Nutrioso, AZ
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Drop chart ?

I have a question about drop charts.
First off my range in AZ is at 2100 ft I blast dogs in northeastern AZ at 8000 ft and I am hunting speed goats back home in WY at 5000 ft My 7mm STW is chrono'd @ 3500 fps here at 2100 it's not mine so I was wondering if fps would change at all the locations I shoot at? I would think not.

Question is do I sight in at my home range and just change my drop charts for the altitude I am shooting at or sight in every time


Thanks
Tony
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Old 02-14-2008, 01:01 PM
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I had often wondered that question too for when I go away on a hunt. I just used JBM calculations and set the zero range at 1 yard and the elevation of 2100 feet. At 200 yards the impact was at 290.2 inches high. When I changed the elevation to 8000 feet, the impact at 200 was 290.3" high (.1" difference). I used 200 yards because that is what I generally sight in my rifle for and adjust from there.

Please correct me if I'm wrong, but acording to that, you should be able to make a new drop chart using your same Zero but different elevations (you could compensate slightly by imputing the .1" differnce in the sighted in range however).
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Old 02-14-2008, 01:24 PM
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Britz

cause your the only one that reply to my posts and we are min bro's (born in Calidonia family In Waconia, Branerd (SP), Hallock, Thief River.) Grew up in Casper Wyoming. Now in Queek Creek and Nutrioso AZ. How ya doing in the COLD it 75 here in AZ today
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Old 02-14-2008, 01:29 PM
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I have also set up using JBM calculations. At my Alt it is dead on.
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Old 02-14-2008, 03:04 PM
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Quote:
Originally Posted by HDTony View Post
cause your the only one that reply to my posts and we are min bro's (born in Calidonia family In Waconia, Branerd (SP), Hallock, Thief River.) Grew up in Casper Wyoming. Now in Queek Creek and Nutrioso AZ. How ya doing in the COLD it 75 here in AZ today
Well, I tell ya. I just loaded up a few batches of 22-250 rds for testing this morning but since it is 3 degrees and 15 mph wind I will likely not get off the couch much today - other than to blow snow. I am a little bumbed since I was hoping to do a bunch of shooting this weekend but it's supposed to be really windy -- oh well.

I have had pretty good luck w/ jbm too after I figured out that my scope adjusted inches per hundred - not MOA.

Take'er easy, Mark
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Old 02-14-2008, 09:00 PM
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Originally Posted by britz View Post
Please correct me if I'm wrong, but acording to that, you should be able to make a new drop chart using your same Zero but different elevations (you could compensate slightly by imputing the .1" differnce in the sighted in range however).
Correct. This is one reason 100 yd zeros are so popular--it'll be even less. If zeroed for 300, 400, etc, your zero will change significantly with altitude so you can't calculate a new dropchart with the same zero.
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Old 02-14-2008, 11:30 PM
CAM CAM is offline
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Hello HDTony
[QUOTE=HDTony;190260]I have a question about drop charts.
First off my range in AZ is at 2100 ft I blast dogs in northeastern AZ at 8000 ft and I am hunting speed goats back home in WY at 5000 ft My 7mm STW is chrono'd @ 3500 fps here at 2100 it's not mine so I was wondering if fps would change at all the locations I shoot at? I would think not.

Question is do I sight in at my home range and just change my drop charts for the altitude I am shooting at or sight in every time

Maybe its the wording,
Your point of impact will change with enviromental conditions, (external ballistics)
Your FPS could change with temperature, but its Internal Ballistics, not covered in external ballistic programs.

You need to chrony your load at different temps to know if your FPS changes and how much, because you need this info to start the exterior ballistic.
3500 FPS @ 2100 asl is not the info you need!

The info you need for the program is (as an example)
3400 FPS @ 0 deg
3500 FPS @ 59 deg
3600 Fps @ 100 deg

Then say the temp is 30 deg you put in 3450 FPS into the exterior program.
then all the other stuff to get your drops.

CAM
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