 Scope adjustment question 

02192008, 01:55 AM

Junior Member


Join Date: Feb 2008
Location: Greeley, Colorado
Posts: 23


Scope adjustment question
I just recently joined the site, great information, great site.
I just recently bought Sierra's infinity software. I am looking at trajectory charts and I am wondering about adjustments for point of impact. For example I ran a chart for a 140gr Nosler Accubond with a 400 yard zero, the software tells me with a 400 yard zero it would be 4.66" high at 100 yards.
Assuming my gun was zeroed at 100 yards would I need to adjust the turret for basically 4.6" up to be right on at 400, removing all other external factors. It seems to simple, the math I mean not the shot, it seems like I am missing something.
The same for 500 yards, @ 100 yards it shows 6.59" high, so by the same logic in a perfect atmosphere if zeroed at 100 yards the correction for that distance would be 6.59" to be dead on at 500 yards.
This is assuming the scope has the room for adjustment.
Am I missing something or is this the correct way to start building charts for a specific load?
ws

02192008, 02:38 AM

Gold Member


Join Date: Jun 2006
Location: ShangriLa
Posts: 913


As long as you are talking about moving that 4.6" or 6.59" on the 100 yard target you are correct. You are just moving the POI up and down.
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02192008, 09:02 AM

Platinum Member


Join Date: Mar 2007
Location: MN
Posts: 1,219


Welcome aboard!
The thing about balistic software is that they are never "perfect" They will get you very close (I should say that they information that you have to enter isn't always right on the spot). Some bullet manufactures list inacurat BC's for their bullets and tradjectory at different altitudes vary. Also, Your actual velocity may be very different from what is listed for the load you are shooting. If possible you should test them with a Chrony. You should always test your load on the range at the distances that you intend to shoot at to correct the differences between what your program spit out and what your bullet actually does. I am not familiar with that program  I just use JBM calc on the net.
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02192008, 05:07 PM

Junior Member


Join Date: Feb 2008
Location: Greeley, Colorado
Posts: 23


Quote:
Originally Posted by woods
As long as you are talking about moving that 4.6" or 6.59" on the 100 yard target you are correct. You are just moving the POI up and down.

Based on a 100 yard zero the chart shows the bullet 18.63" low at 400 yards, then changing the chart to a 400 yard zero it shows 4.6" high at 100 yards, I am making the assumption that his would be the adjustmentbe dead on at 400, in a perfect world.
I understand that this is based in a perfect world and nothing is for shure until I get to the range and varify, but this is just a starting point for me.
ws

02202008, 12:00 AM

Silver Member


Join Date: Dec 2001
Location: Pennsylvania
Posts: 230


You have it right. Shoot a 7mag?
Successful drop charts depend on your scope. If your scope adjusts in inches/100 yd, you will want to just use the inches provided on your program. If it adjusts in MOA the number calculated gets divided by 1.0472.
If it adjusts some weird number it gets divided by that.
However once you start doing it, it won't take long and you will forget the 4.66 and the 6.59 stuff and know 400 = 4.5, 500 = 6.5, 1000 = 23. etc.
I use the divisor of 1.05 (MOA) in my calculations as my Leupold LRT's are very close to that. I shoot a group at 100, dial the scope up 20 numbers and shoot another one. I come up with 21 inches.
If I had came up with 20, my divisor would have been 1.00 for the rifle.
Likewise if I came up with 19, my divisor would be 0.95. Bottom line, match your chart to your scope. And try and adjust the available inputs to closely align your calculated data with your real world results.
Shooting elevated groups also gives you the indication of how well your scope is leveled at the same time. (Provided you drew a vertical line with a level and you are sure your rifle is level.)
Good luck,
Shummy

02202008, 01:04 PM

Silver Member


Join Date: Jan 2008
Location: SF Bay Area
Posts: 210


Sierra Software
Quote:
Originally Posted by Water Swatter
Based on a 100 yard zero the chart shows the bullet 18.63" low at 400 yards, then changing the chart to a 400 yard zero it shows 4.6" high at 100 yards, I am making the assumption that his would be the adjustment be dead on at 400, in a perfect world.
I understand that this is based in a perfect world and nothing is for sure until I get to the range and verify, but this is just a starting point for me.
ws

WS...I have the Sierra Infinity V ( I have not purchased the new version yet) but assuming there are no major changes, I think you are slightly confusing 2 issues...1) inches high under bullet path column at 100 yards and 2) elevation correction for a given range. As far as I can tell your math is good, but the software will do all this for you. You should have 10 columns on your calculated page , NOT 8...If you have 8 columns then go to the "Trajectory" column and click on "dual MOA" ...accept values and then calculate and you will end up with 3 separate columns relating to "Drop" they are "drop in inches" "bullet path in inches" and "bullet path in MOA". The two relevant columns are bullet path in inches and bullet path in MOA
The sequence is... you decide on your zero based upon what kind of hunting or shooting you anticipate doing. (The bullet path in inches will tell you how high the bullet is above POA at any intermediate range...also, play around with the PBR functions under the "Operations" column) Then sight your rifle in at this range using the "bullet drop in inches" column, noting how high the bullet is at 100 yards ( if you are sighting in at 100 yards) and get you rifle to group as closely as you can to this figure (i.e. "x" inches high at 100 yards). There is flexibility here e.g. One of my scopes has elevation correction of 1/2 MOA so sometimes I cannot get to the exact point due to 1/2 minute clicks...but the software can help with this also. You can enter various zeros in the "Zero Range" box and fine tune your chart, ending up with a very close correspondence to the inches high at 100 in the bullet path column and your group on the target. I sometimes end up with zeros of 227 yards or 243 yards or whatever and it makes no diference if you end up with an odd number for your zero.
Then print your chart making sure you have 10 columns . You will then be able to look at a distance to target...and move your finger over to the bullet drop in MOA column ...dial the necessary correction and shoot.
All the other members have given excellent advice...you absolutely must chrono loads, and HoytemanPA has given a very cool way of seeing exactly what your scope does with each click...thanks Shummy! That helped me!
And you are right, this is a starting point. But you can fine tune in the real world. But the software is, in many cases remarkably accurate, and helps save time. Good Shootin' 30338
Last edited by 30338; 02202008 at 01:12 PM.
Reason: premature clickation

02232008, 03:50 PM

Junior Member


Join Date: Feb 2008
Location: Greeley, Colorado
Posts: 23


Quote:
Originally Posted by HoytemanPA
You have it right. Shoot a 7mag?
Successful drop charts depend on your scope. If your scope adjusts in inches/100 yd, you will want to just use the inches provided on your program. If it adjusts in MOA the number calculated gets divided by 1.0472.
If it adjusts some weird number it gets divided by that.
However once you start doing it, it won't take long and you will forget the 4.66 and the 6.59 stuff and know 400 = 4.5, 500 = 6.5, 1000 = 23. etc.
I use the divisor of 1.05 (MOA) in my calculations as my Leupold LRT's are very close to that. I shoot a group at 100, dial the scope up 20 numbers and shoot another one. I come up with 21 inches.
If I had came up with 20, my divisor would have been 1.00 for the rifle.
Likewise if I came up with 19, my divisor would be 0.95. Bottom line, match your chart to your scope. And try and adjust the available inputs to closely align your calculated data with your real world results.
Shooting elevated groups also gives you the indication of how well your scope is leveled at the same time. (Provided you drew a vertical line with a level and you are sure your rifle is level.)
Good luck,
Shummy

.300 Win Mag
Nikon Buckmaster 1/8" adjustments, or was, I am in the market for a new better quality scope. Looking at the Nikon Monarch or Elite 4200.
What is the difference between 1/4" adjustment and 1/4 MOA adjustment? The MOA adjustments are confusing, where can I read up on these adjustments? MOA language is foreign to me, ( If it adjusts in MOA the number calculated gets divided by 1.0472), what number gets calculated?
I use a Wheeler level, level, level to level my scope when mounting a new scope. Is there a beter way then that? It seems fine out to 300 yards but I have not been adjusting the turrets before now
Thanks again for the information.
ws



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