Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Hunting > Long Range Hunting & Shooting

Long Range Hunting & Shooting Nightforce Optics


Reply

Need help with "true velocity" for a drop chart

 
LinkBack Thread Tools Display Modes
  #1  
Old 07-29-2011, 04:23 PM
Junior Member
 
Join Date: May 2011
Posts: 26
Need help with "true velocity" for a drop chart

I'm trying to figure out a drop chart and need to know what the true velocity of my load is. I am trying to do this without a chronograph ( I have a Oehler 35 but I do not trust its numbers).
I'm shooting a 7mm RM. loaded with 180 grain Bergers (stated BC is .672), zeroed at 200 yards. Went shooting this morning to recheck my numbers as the ones I got last week gave me two vastly different calculated true velocities and I figured I must have done something wrong. I ended up with very similar results today. Conditions Wind none, temp 65, pressure 25.20, elevation 4950.
465 yards 5.1" high (5 shot group) using the G7 program the velocity is calculated at 2915. I then move to 753 yards and shoot a group 2.8" low the calculated velocity is 2686. Nearly 250 fps different. Same load, same gun, same shooter. I checked the distances with two different range finders multiple times. These data are very close to last weeks numbers so they are reproducible but they close are far numbers do not correlate. Any thoughts?
Reply With Quote
  #2  
Old 07-29-2011, 06:20 PM
Platinum Member
 
Join Date: Jan 2008
Location: Northeast
Posts: 2,258
Re: Need help with "true velocity" for a drop chart

This might be a dumb question. Are you using the g7, ballistic coefficient of the bullet iin a G7 calibrated program. If you use G7 BC 's with a G1 program you will get screwy velocities. The value. you site appears to be a G1 value. The G7 value is a lower value. I tried what your doing and was able to get pretty close. While it is claimed that the G7 is a better formula, I was able to match up very close to my chronograph using G1. I also have trouble trusting or relying only on my chronograph.
Reply With Quote
  #3  
Old 07-29-2011, 06:42 PM
Gold Member
 
Join Date: Dec 2002
Location: mathias wv
Posts: 985
Re: Need help with "true velocity" for a drop chart

Quote:
Originally Posted by Greyfox View Post
This might be a dumb question. Are you using the g7, ballistic coefficient of the bullet iin a G7 calibrated program. If you use G7 BC 's with a G1 program you will get screwy velocities. The value. you site appears to be a G1 value. The G7 value is a lower value. I tried what your doing and was able to get pretty close. While it is claimed that the G7 is a better formula, I was able to match up very close to my chronograph using G1. I also have trouble trusting or relying only on my chronograph.
agreed, no way the G7 BC for a 180 berger is that high
RR
__________________
Born to Hunt, Forced to Work!
Reply With Quote
  #4  
Old 07-30-2011, 11:09 PM
Junior Member
 
Join Date: May 2011
Posts: 26
Re: Need help with "true velocity" for a drop chart

no i'm using the G1 BC. Just using the "ballistic calculator powered by G7" sorry for the confusion.
Reply With Quote
  #5  
Old 07-31-2011, 10:47 AM
Platinum Member
 
Join Date: Jul 2009
Location: GEORGIA
Posts: 1,190
Re: Need help with "true velocity" for a drop chart

What is the farthest distance you are going to shoot. If you know that answer you could shoot at distances out to 400 or 500 yds and have a custom turret made for that particular load. Then all you will have to do is range the target hold for the wind and shoot.

This is what I did and it worked perfectly:

Drop chart. - Georgia Outdoor News Forum

Testing new Vortex custom turret. - Georgia Outdoor News Forum

gt40
Reply With Quote
  #6  
Old 07-31-2011, 02:04 PM
Junior Member
 
Join Date: May 2011
Posts: 26
Re: Need help with "true velocity" for a drop chart

I understand knowing your gun, but mathematically there must be something I'm doing wrong here.
I doesn't seem practical to shoot a drop chart at every possible elevation combination that I might have (1000 ft for Alaska moose, 2500 ft for Arizona Deer, 5000 ft for Idaho deer, 6500 ft for Wyoming antelope and 8000 ft for elk, then compound that with various temperature combinations that I might experience. Even if I was able to do that my barrel would be ready to be replaced by the time I was finished.
Reply With Quote
  #7  
Old 07-31-2011, 02:12 PM
Platinum Member
 
Join Date: Nov 2008
Location: SW Montana
Posts: 4,437
Re: Need help with "true velocity" for a drop chart

Have you checked your optic for movement value? Are there terrain changes your shooting over or shooting at an angle?
__________________
High Fence, Low Fence, Stuck in the Fence, if I can Tag it and Eat it, it's Hunting!

"Pain is weakness leaving your body"
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: Need help with "true velocity" for a drop chart
Thread Thread Starter Forum Replies Last Post
For those of you "drop chart guys" Nikolakangrga Long Range Hunting & Shooting 2 03-31-2011 09:12 AM
What are "break velocity" and "retard. coeffic. rate"? Monkeyleg Rifles, Bullets, Barrels and Ballistics 1 01-02-2011 12:14 AM
You're favorite "woods gun"? mine proved true today goose Deer Hunting 53 05-11-2010 07:41 PM
"True Ballistic Range" with Leupold rangefinder Bob33 Long Range Hunting & Shooting 2 08-17-2009 11:43 PM
New "true" time of flight device. What do you all think? Michael Eichele Rifles, Bullets, Barrels and Ballistics 11 04-10-2009 09:53 AM

Current Poll
Spot & Stalk or Ambush For Western Deer?
MOSTLY - Spot & Stalk - 73.74%
1,028 Vote
MOSTLY - Ambush - 26.26%
366 Votes
Total Votes: 1,394
You may not vote on this poll.

All times are GMT -5. The time now is 05:15 AM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC