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Drop charts

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Unread 01-05-2013, 08:08 AM
Platinum Member
Join Date: Jan 2008
Location: Northeast
Posts: 3,668
Re: Drop charts

Originally Posted by squirrelduster View Post
Had a strange experience at the range today.
Working up drop charts for my 6.5x.284. Berger 140 gr. 2930 fps through them chrono during load work up, no chrono today.
Shot a golf ball sized rock at 100 yards to verify zero.
Target at 500 yards.
Dialed in 8.5 minutes from my iPhone ballistics app.
Shot high.
Dialed down to 7.5 MOA
Shot high
Dialed down to 6.5 MOA
Perfect elevation. 3 inches to the left due to wind. Compensated and the next two were 1/2" apart. My deer rifle really shoots.
My question is, to get the drops correct the velocity needs to be 3250 fps. I have never had to change my velocity this much.
Anybody else seen this?
Being a 6.5x284 shooter, it is very unlikely that 6.5 MOA is the actual drop for 500 yards with a 100 yard zero. Your velocity of 3250FPS is not right. Shooting a golf ball sized rock for establishing your 100 yard zero is not precise enough for accurately determining drop data out at 500 yards. This is very likely the compounded variation you are experiencing at 500 yards. Having used numerous lots of 140 VLD's it also not likely that the BC of your bullet is that far off the published spec. I don't trust chrongraphs that much but your chronographed velocity of 2930 sounds realistic and even a variation of 50 FPS wouldn't give you the drop variation you are experiencing at 500 yards. I determine the drop data for my 6.5 x284 using a 200 yard zero that has to be nuts on with at least a 1" perfectly centered group. At 100 yards, .5 MOA. The ballistic data/drops, assuming all other variables are entered correctly, using the Bergers are always very close to expectation. IMHO.

"Let us speak courteously, deal fairly, and keep ourselves armed and ready"-T. Roosevelt
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Unread 01-06-2013, 12:05 AM
Silver Member
Join Date: Dec 2007
Location: sebastopol, ca.
Posts: 418
Re: Drop charts

I definitely have more work to do.
The rock shooting was just to make sure the zero didn't move.
I need a trip to a real range that I can shoot to 600 yards. Closest one is 3.5 hrs away.
Probably head to some BLM land next week to rezero at 100 and record drops at 300, 400, and 500. Want to be able to shoot to 1k with accuracy. Have a great load worked up so I need to get my drops correct.
Thanks for all the help.
I will repost with my findings.
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Unread 01-06-2013, 08:42 AM
Silver Member
Join Date: Apr 2009
Location: New Mexico
Posts: 240
Re: Drop charts

Originally Posted by squirrelduster View Post
Winner, the scope is a Nightforce that has been on multiple rifles with no issues before so I doubt if it has anything to do with the problem.
You never know until you test ............believe only what you can verify. If its a nightforce, then nothing's every going to possibly be wrong with it.

This is a trick I learned from a SF guy, the first thing they did with any new equipment set up ( mostly S&B scopes BTW).

Shoot four three shot groups and Prove me wrong, for your own sake! It will only take 12 rounds, good luck with your range session.
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