I don't really care where the chart says I am supposed to be. As long as it is close enough to allow me to test, then I am good to go. I downloaded two different charts for my Swede, and neither was right between 700-1000. Close enough to figure out my actuals though. A dirt hillside with some medium rocks gets you close in a hurry. Then fine tune on steel.
The fact of the matter is that with all of the atmospheric and mechanical inputs entered correctly into a good ballistic program, such as JBM or Ballistic AE which uses JBM, a correct output can be computed. They are known.
The velocity and BC figures are another story
Velocity figures taken from dude's chronographs are not the most reliable. BC's of identical bullets vary when fired from different barrels.
Ballistic AE has features to help you calculate the true velocity and BC of your bullet from actual drop.
Ive never needed to use them. I simply intput a velocity in the starting page that I believe is very close to actual, calculate trajectory, and shoot at the longest plate on our range. I refine my data dialed until I achieve a group of impacts in the center if the known distance target, record that number then adjust the velocity input on the trajectory page until the program outputs the actual drop number at that range.
I then test that drop chart at every distance to confirm accuracy. Works every time.
I will also submit to the board that the velocity figure that produces a drop chart matching actual drop is your actual velocity. I trust its accuracy far more than what a chronograph says.
Originally Posted by Bristoe
The people wringing their hands over Trump's rhetoric don't know what time it is in America.
The fact of the matter is that with all of the atmospheric and mechanical inputs entered correctly into a good ballistic program, such as JBM or Ballistic AE which uses JBM, a correct output can be computed. They are known.
The velocity and BC figures are another story
Velocity figures taken from dude's chronographs are not the most reliable. BC's of identical bullets vary when fired from different barrels.
Ballistic AE has features to help you calculate the true velocity and BC of your bullet from actual drop.
Ive never needed to use them. I simply intput a velocity in the starting page that I believe is very close to actual, calculate trajectory, and shoot at the longest plate on our range. I refine my data dialed until I achieve a group of impacts in the center if the known distance target, record that number then adjust the velocity input on the trajectory page until the program outputs the actual drop number at that range.
I then test that drop chart at every distance to confirm accuracy. Works every time.
I will also submit to the board that the velocity figure that produces a drop chart matching actual drop is your actual velocity. I trust its accuracy far more than what a chronograph says.
If BC values were always accurate and consistent that would be true, as long as all inputs were correct and complete. But as you said, the fact is that BC values vary. They vary with twist rate, rifling finish, number and shape of lands engraving the bullet, etc. As with any scientific data, you can not assume a perfectly linear relationship between a single dependent and independent variable, when there are 2 or more dependent variables at play. If actual drop doesn't match predicted drop, it is either due to incorrect actual BC value or incorrect actual velocity, but it's impossible to say which one for sure without eliminating one variable. That is why Bryan Litz uses Doppler radar to test for true BC values- because the velocity variable is known with reasonable certainty.
I tend to make my chart match reality..... it's a lot tougher to change reality to meet your chart..... unless you're a Liberal.....
Every time I thought a Leupold was tracking 'funky'.... it was my inputs that were off.... once I fixed the loose screw in the nut behind the trigger.... things got a lot more accurate and consistent.
Also.... a small variation in what you presume is a '100 yard zero (or 200... or whatever) can make for much larger errors downrange. Combine a zero that's 1/2" higher/lower.... and a 2-4% error in in chronographed velocities.... throw in a .05"-.10" scope height input error.... some pressure variance.... and you can see pretty quickly how you could have 1-2 MOA variance (projected vs. actual) at 500yds.
That's why, like Rick, I shoot the dope that's most accurate far away.... and accept small variances at closer range, where the differences are much smaller.
You better pray to the God of Skinny Punks that this wind doesn't pick up......
I tend to make my chart match reality..... it's a lot tougher to change reality to meet your chart..... unless you're a Liberal.....
Good one. It's also pretty easy to change scopes and see if a different one tracks differently. Especially when it's just sitting in the safe. You're right about the scope height error input though. I was slightly over-estimating using the default value. When I measured and corrected it (Thanks RC), there was a bigger difference between actuals and predicted. Go figure.
As far as the chronograph, just for fun does anyone have quickload handy?
And yes I know it's just an approximation but I'd be interested in what the output is. If it's closer to RC's velocity of 3025, I'd be interested in knowing that:
.260 Remington shooting a 123 grain scenar, COAL 2.845
Lapua brass with 54.8 grains H20 capacity
23" barrel
48 grains H4831sc
I think those are the inputs, if I left something out let me know.
I shot the 123 Scenar at 3k easily out if a 23" 1-8" .260 using Lapua brass and three or four different powders. You're WAY overthinking this thing....
Rick and I talked about your issue, as I have dope on the exact bullet/cartridge/twist combo.... and it's good dope. I had to adjust the BC and velocity slightly to make the program match actual drops.... but I've never seen a program that reflected perfectly straight out of the gate.
PS....
Bullet : .264, 123, Lapua Scenar GB489 6032 Useable Case Capaci: 46.678 grain H2O = 3.031 cm� Cartridge O.A.L. L6: 2.800 inch = 71.12 mm Barrel Length : 24.0 inch = 609.6 mm
Hodgdon H4831 SC 110.0 47.8 3.10 2981 95.0 62207 10088 1.111 ! Near Maximum !
You better pray to the God of Skinny Punks that this wind doesn't pick up......
Going by what Hodgdon's data center says is a poor indicator of reality
For example, Hodgdon shows the 6.5 Creedmoor with H-4350 and the 140 grain Hornady A-Max at 2.820" COAL with a starting load of 36 grains and a maximum load of 40 grains (Compressed as well)
The velocity range from starting to max was 2464fps to 2660fps in a 24" barrel.
I'm shooting the exact same combination in a 24" barrel. I worked the load up on Saturday. I started at 41 grains and ended at 43.7. The 43.7 grain load showed no sticky bolt and no shiny ejector mark on the case head. The Audette showed a lower velocity node at 41 to 41.9 grains. The upper velocity node was 5 consecutive shots that printed with 1" of vertical at 600 yards. The node was from 42.5 grains to 43.7grains. I loaded the 43.1 grain load in the middle of the node and shot for groups. It shot 3/4" without any seating adjustment. I then loaded 25 to dial in the data.
2875 fps for the velocity input worked perfectly in Ballisic AE
My Comp gun is a 26" barrel with the 139 Scenar. 42.5 grains gives me 2900 FPS...
Last edited by rcamuglia; 10/20/14.
Originally Posted by Bristoe
The people wringing their hands over Trump's rhetoric don't know what time it is in America.
Going by what Hodgdon's data center says is a poor indicator of reality
No doubt. When it matches your chronograph, it's hard to ignore though, at least it is for me. And to be clear, I'm not saying it's right.
Originally Posted by Dogshooter
I shot the 123 Scenar at 3k easily out if a 23" 1-8" .260 using Lapua brass and three or four different powders. You're WAY overthinking this thing....
No doubt I'm over-thinking it, and making some mistakes in the process. I like to make my own mistakes, they make a bigger impression on me than anything else. Thanks for running the QL, if I'm reading that right it predicts 2981 for a 24" barrel, another data point that says my chrono may be a little low.
And I hear you on adjusting the velocity so that it matches the furthest I'll shoot and accepting the smaller error in close, that makes sense. It's off the actuals at 400 by around a half MOA, which I can live with for now. I think RC just adjusted the MV upward to get it to match at 550, I may go back and drop the MV a little and play with the BC to see if I can get a better match at the shorter distances.
