hey guys i just got done putting together my first real custom and i had some questions for yall. Its a 6.5x284 im running lapua brass 57 grains retumbo fed 215 primers and 140 grain vlds. the last two times i shot it for a group it went in the low 2s so the accuracy is there. my question is that i chronoed it and it read 2930 which seems about right. but when i ran my program for a 1200 yard shot using the 2930 velocity it was 9 minutes low. i used a current pressure level and a bc of 612. my question to you guys is which variable do i change to match drops so that i can get some first round hits? thanks for all the help
dope help
- Thread starter Gray R
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RockyMtnMT
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Make sure your scope height is correct. Humidity will also play in there. Muzzle vel is a giant variable. Chronographs give differing information depending on the light at the time of testing. If you are confident in all these inputs then adjust your bc in your program until it matches up with your drops.
I have chased chrono reading in circles. Very tiresome. We got a magneto speed. Now I always feel confident in my velocity input, which gives me confidence to change bc to match drops. The given bc value can be influenced by twist, mv, and altitude. The given bc should get you close enough to make your personal adjustments.
Steve
I have chased chrono reading in circles. Very tiresome. We got a magneto speed. Now I always feel confident in my velocity input, which gives me confidence to change bc to match drops. The given bc value can be influenced by twist, mv, and altitude. The given bc should get you close enough to make your personal adjustments.
Steve
ShtrRdy
Well-Known Member
Something else to check over is the scaling of the scope. It's very possible for a scope to not adjust the exact amount the turret says it should. When you're reaching out a long distance this error can add up when dialing in elevation correction.
Watch this DVD http://www.longrangehunting.com/store/putting-rounds-on-target-with-bryan-litz-dvd.html
The DVD will take a person from prepatory work up through calibaration to include utilizing tested BCs during calibration.
The DVD will take a person from prepatory work up through calibaration to include utilizing tested BCs during calibration.
bigngreen
Well-Known Member
With that much error you need to start back at the start, get all the basic rifle info like scope height, which is usually easy but give special attention to the value your turret moves in, in time you may need to check your turret tracking and get it dialed in even tighter than factory value.
After that load and bullet data, you'll have an easy time with the bullet but I would suggest changing to a G7 BC instead of the G1 value, you should not have to tune the G1 value to 1200 yards. The hardest part is a quality velocity, a Magneto speed or Labradar are awesome but $$, good new is if you take care and nail your other values the speed will be the only value you need to change in the range your looking at.
Temp is important, station pressure is important and make sure you do not use station pressure and elevation in combination as some programs will allow this. Range is also critical as well as shoot angle. From there you have the minor things that will be needed when your fine tuning, humidity, Coriolis, spin drift.
If you post up your values, correction and actual POI I'm sure there are a number of use who would run it and help out!
After that load and bullet data, you'll have an easy time with the bullet but I would suggest changing to a G7 BC instead of the G1 value, you should not have to tune the G1 value to 1200 yards. The hardest part is a quality velocity, a Magneto speed or Labradar are awesome but $$, good new is if you take care and nail your other values the speed will be the only value you need to change in the range your looking at.
Temp is important, station pressure is important and make sure you do not use station pressure and elevation in combination as some programs will allow this. Range is also critical as well as shoot angle. From there you have the minor things that will be needed when your fine tuning, humidity, Coriolis, spin drift.
If you post up your values, correction and actual POI I'm sure there are a number of use who would run it and help out!
Browninglover1
Well-Known Member
9 MOA is a lot. You meant to say 9 MOA and not 9 clicks right?
FearNoWind
Well-Known Member
I have never found any reason to question the BC data published by Berger for its VLDs. For some other bullet manufacturers, yes. Berger, no. I believe you will find your 6.5 140 grain VLDs listed as .612 BC. IMO, you'll do well to stick with that figure until you've got a very good chronograph and data with consistently low SD/ES with which to do a carefully managed analysis on your own.
If your MV assumption of 2930 is flawed you're wasting ammunition chasing long range ghosts. Even at a MV of 2930 fps, by the time that little pill reaches out to 1200 yards it is just barely supersonic so it wouldn't take much to adversely affect its trajectory.
If your MV assumption of 2930 is flawed you're wasting ammunition chasing long range ghosts. Even at a MV of 2930 fps, by the time that little pill reaches out to 1200 yards it is just barely supersonic so it wouldn't take much to adversely affect its trajectory.
Given the info you provided, I don"t think incorrect velocity is your problem. If anything, the velocity of 2930 is on the low end of the expected range for your load, and the low hits you are getting would suggest the corrected velocity would be substantially lower. This is not likely. It would be useful to know what your riflei is doing at a range between 500-1000 yards, what your zero range is, elev/temp conditions, and elevation settng for a specific range.
