Advanced Ballistics Questions Regarding Sean Kennedy's Shooter Program

[RockyMtnHigh]

Please only respond to this thread if you have knowledge of advanced ballistics and/or experience with Sean Kennedy's Shooter Ballistics App. ​

Background Info:
I shoot a Christensen Arms 300 RUM. I am using a Schmidt & Bender 4-16 x 42 PM II LP scope with single turn 0.1 mrad click values. I am confident the scoping is tracking correctly. I'm zero'd at 100 yards, and I have accurate zero data including a zero atmosphere which includes station pressure, temperature, relative humidity, etc.

Issue:
I am not getting ballistic solutions that match my target data once I get over around 500 yards, and I have no idea why. My rifle profile is 100% correct; I even confirmed my sight height to the nearest hundredth of an inch. My bullet profile is 100% correct as well. I am shooting a custom load, 180 grain Nosler Accubond bullet. I am using Bryan Litz's ballistic profile, i.e., a BC of 0.246 with the G7 drag model.

I am shooting at accurate, known distances, but once I get over 500 yards Shooter is calling for too aggressive of come-up values. For example, I shoot U1.9 mils at 500 yards, but shooter calls for U2.0 mils. I know this seems petty but it gets worse, obviously, at longer distances. For example, at 800 yards Shooter calls for U4.3 mils, but I actually only need to come up U4.0 mils, and that 0.3 mil difference amounts to 8.64 inches at 800 yards! 1,000 yards is a train wreck when using the Shooter produced data and all of this is made worse when I shoot at very high elevation or make extreme changes to the current environmental conditions.

I have tripled checked every input, and I am accurately measuring environmental data with a Kestrel 4500. The only variable that can possibly be causing this is the muzzle velocity. Unfortunately, Shooter does not allow you to enter actual muzzle velocities for known temperatures. Instead, the program allows you to input what it calls "velocity variation." This is a fancy way of saying you calculate the change in velocity in feet per second and divide by the change in temperature in order to establish a ratio. The issue is I know this ratio is not linear, but rather logarithmic, so it's not accurate - more of a best guess really. I have logged actual muzzle velocities for a range of different temperatures, but it doesn't do me a lot of good if I can't input the data into the program itself.

So far, I have discovered two options for forcing Shooter to calculate a ballistic solution / drop chart that matches (or gets pretty close) my actual range data. The first way I have accomplished this is to essentially back solve for a velocity variation that creates a drop chart that matches my actual shooting data. In other words, use trial and error and input various velocity variations that spit out solutions that match my data.

The second option is to use the velocity calibration feature, which allows you to input actual come up values for known distances and then let the program do its own computation of adjusted muzzle velocity. This appears to me to be less accurate than the first option I just described though because, for example, when I shoot U4.0 mils at 800 yards instead of what shooter calls for, which is U4.3 mils, it calculates an adjusted muzzle velocity several hundred feet per second slower than what my chronograph consistently captures.

Questions:
1) Am I missing something very obvious?
2) How accurate are these ballistics programs typically? Am I asking for an unreasonable level of accuracy?
3) If I use the ballistic solution that I have created by using option #1 above (back solving for velocity variation), can I expect my solutions to be accurate going forward? i.e., can I use this as a baseline solution, and, therefore, make changes to environmentals, etc. later and expect an accurate output?

Thanks

 

[kswgb]

I was going to post a very similar question tonight as well. Last weekend, we went to the Whittington Center to shot long range and I had very similar problems. We shot the buffalo at 1123 yards with a 223, 308 and a 300WM in all cases Shooter gave us a ballistic solution which was too aggressive. We needed on average a mrad less come up for each rifle. The error increased on the Barret Unknown Distance Range. The 50BMG needed 1.5 mrad less come up and the 300 WM needed 2 mrad less come up at 1836 yards (the closest target - the red human silhouette). I played with velocity, elevation, temp and still no dice. At this moment I have lost a lot of faith in this program due to its inability to provide an accurate ballistic solution. Is there a variable I am overlooking? Are there other better programs for shooting beyond 1000 yards?

 

[bigngreen]

The program is accurate enough to provide a good solution well beyond what's being shot in this thread, look very hard at tuning the turret value if you think you have everything else nailed.

 

[RockyMtnHigh]

The program is accurate enough to provide a good solution well beyond what's being shot in this thread, look very hard at tuning the turret value if you think you have everything else nailed.

I agree that it should be capable of providing a solution beyond the ranges I'm describing. I just calculated the elevation correction as 0.93023256 meaning that my scope could have click values representing only ~93% of a true click. This is based on just one observation taken at 800 yards, and I find it hard to believe that a quality scope like a Schmidt & Bender would be that off. The interesting thing is that the ballistic solution I arrive at after correcting for the elevation factor is very, very close to what I got when I back solved for the velocity variation. Is there a very accurate way to check your turret values? Is this preferable to me adjusting the velocity variation? Am I using the velocity variation correctly?

Thanks again. I hadn't thought about this because when I first tested the scope for tracking out of the box at a close range it was more or less right on. I guess if it's just slightly off that is exacerbated at longer distances.

 

[barnesuser28]

I agree that it should be capable of providing a solution beyond the ranges I'm describing. I just calculated the elevation correction as 0.93023256 meaning that my scope could have click values representing only ~93% of a true click. This is based on just one observation taken at 800 yards, and I find it hard to believe that a quality scope like a Schmidt & Bender would be that off. The interesting thing is that the ballistic solution I arrive at after correcting for the elevation factor is very, very close to what I got when I back solved for the velocity variation. Is there a very accurate way to check your turret values? Is this preferable to me adjusting the velocity variation? Am I using the velocity variation correctly?

Thanks again. I hadn't thought about this because when I first tested the scope for tracking out of the box at a close range it was more or less right on. I guess if it's just slightly off that is exacerbated at longer distances.

Shoot a 3 or 5 shot group at 100 yards, dial 8.4 mills, measure how far apart from center to center they are. Do the math and you will have your error.

 

[RockyMtnHigh]

Shoot a 3 or 5 shot group at 100 yards, dial 8.4 mills, measure how far apart from center to center they are. Do the math and you will have your error.

I feel like there is just too much potential for shooter error when we are talking about such small numbers. Even with a lead sled I can't accurately replicate those shots, and I understand you're point about shooting a whole group and maybe looking at an average.

I think I may have unlocked part of the puzzle. In Shooter, when you use a Bryan Litz bullet profile, it is only populating the average ballistic coefficient for that particular load. For my bullet, the G7 BC is 0.246, which is what he publishes as the average BC on page 509 of his book Applied Ballistics for Long Range Shooting, but if you look at the data he presents he provides a list of BCs for this bullet based on a minimum muzzle velocity. Regardless of temperature and pressure, I have never recorded a muzzle velocity less than 3,000 fps. According to his data, my bullet has a G7 ballistic coefficient of 0.253 instead of 0.246. When I input this BC into Shooter my solution changes nominally, but in the right direction.

I understand the need to check my click values, but can anyone weigh in on the muzzle velocity issue / question?

 

[royinidaho]

Been here and done this. The tee shirt is full of holes.

You are headed in the right direction.

The "Shooter" program is trustworthy for many users, including me, to well beyond the mile mark and all distances between that and zero distance.

I started by doing actual drops at accurately measured distances out to 1000 yards.

I then plugged distance and drops in MS Exel and did the curve fit thing. The resulting eq'n was spot on at all distances under conditions identical to the conditions the day the drops were calculated.

This method disregards all specific (important) variables. Barometric pressure, temperature, elevation, velocity and all other variables. A great exercise but completely useless for real world use.

Our most untrustworthy piece of equipment is the chronograph. I use a Beta Chrony and only then for Extreme Spread for a given string of shots. Velocity measurements can only be considered "in the ball park." Tilt it slightly between shots/sessions and things get pretty spread out.

Variable bc is the better way to go. Each rifle barrel creates a different bc as compared to another barrel with the same bullet.

It takes a bit of shooting to determine long range bc changes. If the rifle is ELR accurate one or two shots at each distance is adequate.

Variable bc and "fudging" MV will get you spot on for as small of target as you desire at any range.

I think it was winmag that said "Who cares what the MV used by the program is, just so you hit what you're shootin' at." I concur.

With my two ELR rifles, Shooter inputs were very straight forward and have been validated in various elevations, temperatures, atmos pressures, shot angles and distances to ELR.

However, my 270 Win is another story. I have to knock off 200 to 250 FPS MV to get drops to line up with software predictions.

This just popped into my head and was the final "precise" input that brought things together big time.

How accurate is you line of sight/line of bore measurement? This is a straight forward measurement for non-canted scope mounts. And needs to be "fudged" for bases that are canted.

When this value is "off" affects get worse as distance increases has been my experience.

HTH and keep at it.