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Need some help with my exbal program.

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Unread 04-03-2008, 05:48 PM
Silver Member
Join Date: Dec 2007
Posts: 322
Need some help with my exbal program.

I just started using my exbal program the other day,and I am having problems coming up with a velocity/b.c. combo that works for various ranges.I am shooting a 300wm with a 240gr smk.According to sierra,the b.c. is .711,and according to my chronograph,I am shooting 2480fps.I am sure my chronogragh is reading low,so I started playing with the velocity numbers and I can't get things to add up.I am zeroed at 200yds.,at 300 yards I dropped 8''.I then shot 492 yds,and was hitting pretty much center with 33 clicks elevation(1/4 moa).Then I had to elevate to 90 clicks at 810 yds.Based on the info. I have,is there any way I can get this mystery figured out?
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Unread 04-03-2008, 07:30 PM
Platinum Member
Join Date: Jun 2005
Location: Yakima, Washington
Posts: 3,775
Where you are shooting is there any canyon, cross canyon, elevation change or wind that could be affecting your shooting in any way?

Do you have access to anyone that has a quality chrono?

What scope and mounts are you using?

How did you determine the yardages?

Last edited by ss7mm; 04-03-2008 at 07:58 PM. Reason: added question about yardages
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Unread 04-03-2008, 08:00 PM
Silver Member
Join Date: Dec 2007
Posts: 322
I am shooting in Ohio,very flat.I don't have access to a good chronograph,just the cheap one that I have.I am using a nightforce scope,bases,and rings.How much can published B.C.'s be off from actuall B.C. results?I am using a bushnell elite LRF also.I thought everything was good,I figured I was shooting 2660fps,with a b.c. of .711(sierra'a claim),that worked at 300 yds and 492 yds.But when I shot from 810 yds,I was about 10 clicks(1/4 moa) too low.

Last edited by KQguy; 04-03-2008 at 08:11 PM.
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Unread 04-04-2008, 05:28 AM
Junior Member
Join Date: Jul 2007
Posts: 29
".711 @ 2150 fps and above
.702 between 2150 and 1800 fps
.685 @ 1800 fps and below"

Remember to input all three values.
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Unread 04-04-2008, 06:08 AM
Join Date: Jun 2007
Location: Wyoming
Posts: 2,839
Have you done a box test?
This is at the bottom of the list to check but good to do anyway.
NF's have a great reputation for tracking integrity, but you would eliminate one more possible variable.
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Unread 04-04-2008, 08:01 AM
Silver Member
Join Date: Aug 2007
Location: bismarck ND
Posts: 406
i have had my bc change dramaticlly before. if i were you i would check tio make sure that all of the info that you are putting in the exbal is correct. double check barametric pressure and temp. you can also use altitude and temp. when you are shooting to 800+ alot of things can change. when you shot to the 800+ yard target how was the group. another this is when you change your bc to show the correct moa on the 800+ shot what did it do to the other 2 ranges. alot of the time when you change the bc to correct al longer distance you will see that it wont affect closer shots. that just my $.02.
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Unread 04-04-2008, 10:09 AM
Join Date: Feb 2007
Location: Buffalo, Wyoming
Posts: 1,707
did you enter center of bore to center of scope for the height of scope above bore ?
Lightforce Lights Dealer
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