Range Report Real world dope - issue

[john_1182]

we have had out first real nice day in ages so i was out today with the .223 and i have some confusing real world dope

@ 100 yards dope spot on
@ 430 yards dope spot on
@ 640 yards dope shooting 1 mil high

(ranged with a bushnell yardage pro rifle scope)


i am using bulletflight for the itouch and the current load set up i have in has done me fine up untill now, i was shooting into a 15 MPH head wind from one hill top to just under another hill top, would this create enough of a up draft for me to require 1 mill less elevation?


P.S. the angle i was shooting at was level (say under 10 degrees) so i have ruled that out...

 

[Sterling Shooter]

Re: Real world dope - issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: john_1182</div><div class="ubbcode-body">we have had out first real nice day in ages so i was out today with the .223 and i have some confusing real world dope

@ 100 yards dope spot on
@ 430 yards dope spot on
@ 640 yards dope shooting 1 mil high

(ranged with a bushnell yardage pro rifle scope)


i am using bulletflight for the itouch and the current load set up i have in has done me fine up untill now, i was shooting into a 15 MPH head wind from one hill top to just under another hill top, would this create enough of a up draft for me to require 1 mill less elevation?


P.S. the angle i was shooting at was level (say under 10 degrees) so i have ruled that out...



</div></div>

The error as described is consistent with slope error, and unless the line of sight and target are indeed horizontal, there will be error at the sort of distance you described without countering for it.

 

[AQC440]

Re: Real world dope - issue

There is a lot going on with this question, but I am going to say NO! With-out knowing bullet weight and velocity,and all the variables it is impossible to give an absolute answer. I understand your thinking that the wind hitting the hill directly in front of you causes a vertical wind that effects the bullet for its total flight. But, if that were the case you should have noticed "some" deviation at the 400'ish yard range as well.
Some of the 15 mph wind slamming into the vertical service is absorbed or defused, so you don't get the full value. Guessing, the vertical lift of maybe 2 mph you would have at most a +.2 mil POI...just my .02.
Someone here probably has a more scientific and provable answer and will correct both of us soon!

 

[Greg Langelius *]

Re: Real world dope - issue

Where wind eddies are concerned, no ballistic program I know can predict an accurate path through them. Programs make assumptions that conditions remain constant along the entire trajectory, deliberately limit wind inputs to but a single one, and allow no inputs for up/downdrafts. So logically, they cannot cope with significant conditions variances between shooter and target.

Its a wild world out there, and now would be a good time for you to recognize that calculations can only predict outcomes in a perfect world. Ours is not perfect. Consider them more a set of guidelines than an oracle. Every shot is a bet.

Once the air currents have had a bit to work on the bullet, all bets become less and less secure.

Greg

 

[john_1182]

Re: Real world dope - issue

sorry for the lack of info in the OP for those who asked.

it was a 55grain winchester FMJ @ 3160 with a SD of 20. temp 23.5c (74f) humidity 42% air pressure 1020mb (30.12 inHG)

as for angle to target. there was no large angle to target, i would consider it "flat" but even if i put in 20deg its only a 1/3 mil not the 1 mil i was encountering.

as for the gully i was shooting across the hill i was shooting from was aprox 60deg slope down with a flat of 200 yards and a aprox slope of 30>40 deg up, getting steeper the higher it went up the hill.. hill heights aprox 100 and 150 feet.


Greg i do agree 100%, i just found it strange where the rounds were landing, but as its said "believe the bullet"

 

[Sterling Shooter]

Re: Real world dope - issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: john_1182</div><div class="ubbcode-body">sorry for the lack of info in the OP for those who asked.

it was a 55grain winchester FMJ @ 3160 with a SD of 20. temp 23.5c (74f) humidity 42% air pressure 1020mb (30.12 inHG)

as for angle to target. there was no large angle to target, i would consider it "flat" but even if i put in 20deg its only a 1/3 mil not the 1 mil i was encountering.

as for the gully i was shooting across the hill i was shooting from was aprox 60deg slope down with a flat of 200 yards and a aprox slope of 30>40 deg up, getting steeper the higher it went up the hill.. hill heights aprox 100 and 150 feet.


Greg i do agree 100%, i just found it strange where the rounds were landing, but as its said "believe the bullet"</div></div>

You're shooting a long way out there for your 55 grain bullet; but, setting that aside, proper analysis would suggest angular error. Angular error increases with distance. In your case, butt-to-shoulder, as well as stockweld inconsistency could easily create the error you describe. Perspective of aim could also be inconsistent, promoted by something less than a consistent muscularly relaxed stockweld with the full weight of the head resting on the comb.

 

[Bronco]

Re: Real world dope - issue

2 ft. high at 640 yd. is a lot of deviation. Part of the problem may be with the bullet, poor choice for that distance. RSI comes up with 4.9 mils elevation @ 650 and velocity in the 1350 area.

How many shots did you take at this range and what kind of groups were you getting?

 

[Sterling Shooter]

Re: Real world dope - issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bronco</div><div class="ubbcode-body">2 ft. high at 640 yd. is a lot of deviation. Part of the problem may be with the bullet, poor choice for that distance. RSI comes up with 4.9 mils elevation @ 650 and velocity in the 1350 area.

How many shots did you take at this range and what kind of groups were you getting? </div></div>

The only thing that is known for sure is that the barrel was pointed in the direction of the impacts. Since the rifle always shoots in the direction it's pointed, what's also certain is that the OP, not hitting exactly where aimed, did not know where the rifle was pointed. Not knowing where the rifle was pointed, if not originating with a mis-adjusted sight/s, means, for the result described, the shooter's position was not likely consistent between distances/shot strings. Remember too, although, fundementally, marksmanship is no different for shooting at 50 feet, or 1000 yards, distance does demand perfection. Contol of position, and sight alignment, if not perfected, create angular error which will unmask itself as distance increases.

 

[Lowlight]

Re: Real world dope - issue

Shooting one winter at Thunder Ranch with Clint Smith, we were pushing his "Hammer" out to about 1200 yards and using 168gr SMKs. At the target we noticed several impacts that landed about 20ft above the target. Fortunately a light snow began - wind was gusting just above 15 mph during this series of shots.

We could see during several gusts that the snow was rising up the hillside as the wind came down the valley and impacted against the hill, it traveled up carrying the bullet well above our target.

So I would say it is possible to experience this. We continue to shoot under these conditions to further observe the results down range. Hits on the target could be followed by an impact several feet above the target depending on the severity of the wind gusts.

As Greg stated, your dope is just a starting point. It's nothing more than Data On the Previous Engagement and not to be taken literally from day to day. You always have to believe the bullet as it is has the final word.

Once you venture beyond 400 yards, environmental conditions will effect the bullet flight, wind, temperature, barometric pressure manipulate the flight of the bullet. Many shooters will dope the wind from shot to shot, but very few consider the changes in temperature or barometric pressure will make. We like to use Density Altitude as it is one number that gives us a very good representation of the environmental differences. For example, if you establish your dope at 9AM with a Density Altitude of 1000ft, then next week you shoot at 3PM with a Density Altitude of 3000ft you can expect a difference in your dope / data from the previous weekend.

As you get closer to 1120fps, you begin to lose predictability with some rounds. Being in the 1300fps range, you are on the backside of the ballistic curve, so performance will suffer if your bullet is not up to the task.

 

[john_1182]

Re: Real world dope - issue

thanks everyone, i realise pushing the 55g this far is getting to the extreme of things, but ive also been kmnown to shoot the 40 grain a-max out to 750 yards for giggels, also i have a .308 and some crap tastic winchester power points wich required 62 moa to 1075 yards and go subsonic at 650 yards.. (still group 1/2 > 2/3 mil at that range)

as for shooting position npa ect i was getting fairly decent groups with the .223 at the 640 ayrds range, aprox half mil with the odd flyer high...

.. one thing i just thought of is the scope i was using (busnell yardage pro) (built in LRF), has no paralax adjustment and an incorect sight aligment will throw the shots, but i can only assume that would be the odd shot i had going high.... i if the weather holds up again later today ill go out again and shoot again. 640 yards in the same direction. and 660 yards in the oppisite direction along flat ground and see what happens. it might be a BC issue ?

**air pressure, humidity, were upto date within 30 min of shooting and air temp and of course wind speed were upto date just prior to shooting

 

[vman]

Re: Real world dope - issue

John, as lowlight has said you always have to believe the bullet as it has the final word.

You might go out and find everything is behaving differently.

Have you set up a wind flag down range? I would put money on it that if you had 2 or 3 wind flags down range, one at your position, one mid way and one at 500 yards, you would have varied winds on all 3 flags.

You might assume that the conditions remain constant thru but in the majority of cases different winds downrange will modify the trajectory you get if you have only accounted for near winds.

 

[Sterling Shooter]

Re: Real world dope - issue

OP,

You mentioned that your scope does not have a parallax adjustment. At the distance you're shooting, 3 minutes of parallax error would certainly be possible with the eyeball in a different relationship with the eyepiece than from where the eyeball was upon initial zeroing. Adding a somewhat divergent stockweld and butt-to-shoulder relationship to the scenario would preclude any understanding for where the barrel was actually pointed.

 

[john_1182]

Re: Real world dope - issue

with the combination of, angle to target, no parallax adjustment , wind and good old shooter error i have prity much worked out what was going on. thanks for all the input

 

[Greg Langelius *]

Re: Real world dope - issue

I can concur with LL about shootIng in a snow event.

Had a match once back at Cherry Ridge in the 1990's that ran in November, and heavy flurries accompanied the event. Big fat snowflakes, and enough of them to periodically obscure the targets at 300 yards.

Always known for weird air currents, the weirdnesses of the Cherry Ridge range became a lot more understandable that day. I think it might have even helped me somewhat.

Greg

 

[Goose375]

Re: Real world dope - issue

dont try to get the ammo to match the calculator, get the calc to match the ammo. I use the same app and have the same issues.. Ill adjust the BC or the velocity or weather to get a closer trajectory