I am having issues with updating my range card for my 300 WM. I cannot get the computer calculations to come anywhere close to matching reality. I have three known target distances. 300, 425 and 615 yards. The rifle is zeroed at 300 yards. When I shoot at 425, I add 15 'clicks" of elevation and at 615 yards I add 46 "clicks", to hit the target. When I run JBM and Hornady I come up with similar results, showing that I need to add 2.8 MOA and 7.5 MOA respectively. This in no way matches real world data. For my entry data I am using 1000 feet elevation, .474 BC, G1 drag, for the 180 PT, 3000 fps, 70 degrees, 29.53 (hg), and 1.5 in of sight height. So in essence the rifle doesn't shoot as flat as the computer generated data by a large margin. I have finessed the data and have verified the distances several times, but cannot come close. Any idea's as to what is going on here?
Help with range card
- Thread starter Elkman
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- #3
Ridgerunner665
Handloader
- Oct 28, 2008
- 2,513
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Wrong BC...
Use .359 G1 ...you can tweak that a few points in either direction to get a perfect match to "your" components.
.359 is the BC of the 180 PT as measured in live fire testing at long range by Bryan Litz....some of Noslers advertised BC's are pretty darn close (160 AB, 129 ABLR), but most are not.
Not at all a slam against Nosler...just a proven scientific fact.
Use .359 G1 ...you can tweak that a few points in either direction to get a perfect match to "your" components.
.359 is the BC of the 180 PT as measured in live fire testing at long range by Bryan Litz....some of Noslers advertised BC's are pretty darn close (160 AB, 129 ABLR), but most are not.
Not at all a slam against Nosler...just a proven scientific fact.
longrangehunter
Handloader
- Jun 19, 2011
- 1,476
- 4
Unfortunately making a range card off DOPE, (Data On Previous Engagement) is old school, and not being used anymore because the BC's are off, and so can the ballistic programs being used based on the wrong data.
What's being done now is finding the actual algorithm the bullet’s flying on, called truing.
Basically working backwards from the furthest out you can shoot, like at the transonic zone of the round being used. Doesn't matter what the BC is doing or the MV from a chronograph since the algorithm is tracking perfectly because it was calculated by time of flight, and the MV was done backwards from that data. You'll need to use a custom drag model like what's found on a Kestrel with the Applied Ballistics program.
What's being done now is finding the actual algorithm the bullet’s flying on, called truing.
Basically working backwards from the furthest out you can shoot, like at the transonic zone of the round being used. Doesn't matter what the BC is doing or the MV from a chronograph since the algorithm is tracking perfectly because it was calculated by time of flight, and the MV was done backwards from that data. You'll need to use a custom drag model like what's found on a Kestrel with the Applied Ballistics program.
Ridgerunner665
Handloader
- Oct 28, 2008
- 2,513
- 288
Yep...
Funny thing is...I was doing it that way 30 years ago, lol.
That is, I did the shooting at distance, figured out the drops/windage, and kept notes.
The reason I say that's funny... Because it wasn't long ago that I suggested that method to someone that didn't have all the sophisticated toys to help him.... And all I got for it was laughed at (it wasn't on here).
Granted, it is much easier to do with all the goodies we have today.... But it is not impossible to do without them either.
Sent from my XT1585 using Tapatalk
Funny thing is...I was doing it that way 30 years ago, lol.
That is, I did the shooting at distance, figured out the drops/windage, and kept notes.
The reason I say that's funny... Because it wasn't long ago that I suggested that method to someone that didn't have all the sophisticated toys to help him.... And all I got for it was laughed at (it wasn't on here).
Granted, it is much easier to do with all the goodies we have today.... But it is not impossible to do without them either.
Sent from my XT1585 using Tapatalk
- Thread starter
- #7
Thank you all, this evening I will work through all of those options. I cannot believe that a 300 WM with a stiff load of H-4350 is going slower than 2800 fps but as I said I will try all of the above and see how it works out. As suggested I could shoot at some mid ranges and fill in the blanks, but I refuse to drive 30-40 miles to do the same. I am blessed/spoiled to be able to shoot out my back door, but there is a lot of sky between my shooting position and the three distances, thats why they are exact. My 7MM Mag shoots exactly with the ballistics calculator, so I know that I will make this work satisfactorly.
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- #8
jimbires
Handloader
- Aug 16, 2011
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the easiest way I've found to measure scope height is to pull the bolt back until it's even with the scopes eyepiece bell . then measure from the center of the scope to the center of the bolt . don't use a caliper , it could scratch the scope lens trying to measure this . from what I've seen it's not a super critical measurement for a ballistic calculator . so on this input , a close measurement is close enough .
this pics a little blurry , but gives the idea .
this pics a little blurry , but gives the idea .
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- #12
TackDriver284
Handloader
- Feb 13, 2016
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I usually put a Dewey rod from the muzzle end, just use a straw to protect the muzzle while sliding it in all the way to the magazine area with bolt open and measure from the rod to the center of the scope. But Jim's idea is a good one, never thought of that either.
jimbires
Handloader
- Aug 16, 2011
- 3,151
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you're welcome fellas . it's the KISS method
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