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creating Drop chart

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 07:56
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Optics GrassHopper
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 >>Whacko<<<

I am just starting out getting into shooting rifles and I want to create a drop chart out to 5 or 600 yds. -- what is the most effective process to create a drop chart – my thinking is messed. After zeroing to a solid 100 yd zero, I want to keep the same point of aim (100 yds) but increase my distance. If I either move my line of departure, or move the target (poi) I am not going to get a ‘real’ reading.. If I shoot at targets incrementally moving them out 50,100,150,200 yds and so on..my POA will change and thus the ‘drop’ will not be accurate for a consistent POA(100-yd zero) .. I am thinking theoretically I want to keep the same POA at all distances (50-yd increments) this is messing with me or am I missing somehting (probably the latter)– can someone explain this process? Whacko  thnx a million..

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 08:08
Dale Clifford View Drop Down
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go to this web site
plug in data
print out on card
but first
 
any process you use will require some data before getting started, velocity of bullet, bc, wt. cal.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 08:27
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ok to further clarify myself (hopefully), I want to create a chart for a specific gun in a scpecific load (i did this with software but am at the point that I now want to confirm it) -

 I basically want to take the flight path of the bullet at about 50-yd increments using the same POA (of 100 yds), how does one accomplish this, OR do I simply zero to 100 (or 200), then start shooting groups at 50, 100, 150 etc aiming dead center at each distance target and record where the bullet hits on each target ? actually, this is where the confusion comes in ..

 

Ideally if I could hold the rifle dead on center mechanically at 100 yds (using a 100-yd zero) and set up targets at 50-yd increments along the flight path out to 600-yd, I could technically record the bullet path with one shot.. obviously this is not possible as the first target would throw off the true path of the bullet and so on and so forth..

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 09:33
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To do it right you will need to shoot at those distances.  Start at 100 and then work your way out to 500 and back down to 100 and then back to 500 again do it several times shooting 5 shot groups at each distance.  Make sure you are getting the exact same point of aim, make sure you are mounting the rifle the exact same way every time.  If you shoot 100 yards prone then shoot them all prone.  Don't switch back and forth from bench to prone as that can affect your POI. 
Software will only get you close and then you will need to shoot at all those distances and keep a log of how much elevation adjustment you used to reach each distance. 
Just measuring the drops and then shooting them all at 100 won't really work any better than the software because your bullet is not actually flying the full 500 yards and all the environmental effects that happen at 500 yards will not happen so you will not know for sure how that bullet will react at 500 yards.

Once you figure out your MOA drop at each distance then it will be very easy to create a trajectory chart and a drop chart.   But if you want to do it right, you are just going to have to shoot at all those distances.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 09:34
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You are making a very simple matter very complicated. Even I am confused!!
To check the actual flight path against a calculated one you have to zero the rifle at the same zero distance you used during your calculations. Then, on a level range, set out your targets at the desired distances you wish to check the actual flight path. Aim for the same place on each target as you did when zeroing the rifle and fire away. Measure from your point of aim to the verage of the grouping fired, and that will be your bullet drop over each distance.
When you are aiming at the same point as on the zero target, you are looking in a straight line, as if you are looking through all the targets placed one after the other. Light does not bend. Your bullet however travels in an arc, and will strike each target in a different place, depending on the distance the bullets have to travel.   


Edited by 8shots - March/12/2008 at 09:35
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 10:13
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thanks supertool73, makes sense - I needed a brain check. Actually, a little overthought on my part (or underthought, ha) – I was thinking my POA at each distance will throw off my true trajectory chart and thus my actual drops would not reflect my calculated ..  in actuality, the POA for each distance is considered the same straight line wherever gun is positioned, and thus reflects a constant line of departure, whether at 100 or 300 or 400 yd ranges(aiming dead center at each distance of course), as long as (like u say) the ‘delivery’ method is consistent and you have a solid zero. Don’t know how I messed this one up. I will try it as you explained, except I only want to measure the drops, not make adjustments right now.. thanks..

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 10:25
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sorry to confuse, 8shots. Head%20Banger
consider me set straight.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: March/12/2008 at 14:56
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the only thing that would be different are errors in your equipment, the traj, can only be what it is by the inputs. the flight characteristics of the bullets change somewhat after 500 yds, which can affect the drag profile you used in the program. , but if your equipment, (particularly the scope clicks) is on the difference between the program and your actually impacts will be less than say the extreme spread on your loads velocity, (which will affect it the most at long ranges.)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/03/2008 at 17:32
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Here's how I would like to do it (may not be possible); your available equipment and environmental situation may vary...

1) Set your 'zero' at 100 yards/meters (as you prefer). For a .308, I might personally zero at 200 yards for long work like 600+, so keep that in mind. I believe the standard procedure for military .308 'sniper' rifles is a 200 meter zero.

2) Set identical targets at 50-yard/meter intervals beyond the zero target. I suggest those nice 100-yard bullet drop sighting-in targets that used to come from the NRA (I assume they still do?). This makes MOA calculations a snap, especially if you work in yards (you can always convert to meters later, plug the data into excel, and then tick off the ranges in meters from the ballistic line created on your graph) One caveat is that those targets have a grid, to find elevation and windage adjustments, that may or may not help you if you are or are not dialing in the windage.
 
2A) I think it is important to know the wind value at all your ranges. When placing your target, use a wind gage to be most accurate (available at boating stores among other places) because sometimes that full-value wind will do strange things. Ideally, a zero-value wind (head-on or dead away) would be best for this experiment; however having the ability to shoot 1000 yards in any direction (flat) to eliminate the wind may be difficult... I might suggest dialing in the wind, so you can stay on the paper with the cross hairs on your X. You have to make the call on that one- I think it would be better than holding-off, at least to establish your drop...
 
3) collect data and place in excel. Create graph (log curve should fit best, but play with it to see what makes sense) to create a reasonably accurate flight path. The more data points, the better, obviously!
 
4) your gun 'fixture' needs to be quite solid. The least movement will throw everything out. I think 1" and 100 yd is 0.001" in the reticle of error. (A human hair is three times that for reference) Correct me if wrong on that, but it sounds about right to me. Plus, you will get tired after 25 rounds or so, and start to get sloppy as your range increases. Not a good mix for this type of work!
 
Note that some rounds will climb at certain distances, even though that is counter-intuitive. This is why I think knowing your wind value at each distance is critical, as is a VERY solid mount (was that me who flinched at 850 yd or did that round actually climb???). You may record more or less actual drop than you really have. When I was first going over the .308 ballistics charts (military issue). I noticed the trend was not always dropping, so I asked the question of my instructor, and he confirmed yes, they will climb under certain conditions.
 
But, to answer the question, set your zero (where you expect to do your most shooting) and fill in the blanks from there. If it is 200, you can still shoot 100 and add that data to your chart don't forget. A chrono of speed at each distance (check POI before you shoot your chrono) would be wort the cost of the chrono (once you do shoot it) for sure. So if you hit 7" low at X distance and your velocity dropped by Y amount, you can REALLY get a handle on what is going on out there. Obviously, there is a risk that you shoot five at a 7" drop, set up your chrono and shoot one with an 8" drop (OUCH!)
 
Also, another wrench: do you shoot cold, clean bore, or warm, dirty bore, or combinations thereof? These things become more and more critical as you go down-town with the range. Bullet angle (seated in the cartridge) off by mere thousandths of an inch can greatly affect things down-range too... A lot to consider for a 'simple' ballistics chart. Needless to say, your ammunition better be up to snuff, and as consistent as hell's average temperature...
 
What makes the most sense? Collect as much GOOD data as you can get, and plug it into one of the on-line ballistics charts, and then test the predicted POI to the actual POI. That will probably be easier, and likely what I will do myself... If you change anything about anything (load, head space, projectile etc.) you will have a good base to work from, but will need to reconfirm your zero at range for sure...
 
Sorry if long-winded, but I am in the middle of sorting through all this stuff right now- and there is a lot of it. I will make a similar chart, but with a .22LR out to 100 yards just because it easier (and I need to know for practice)!
 
PS My head hurts...WhackoWhacko
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/03/2008 at 21:47
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When you start actually shooting at long distance, you will find that the theoretical is not as accurate of a predictor of reality as you now believe.  For example, if your scope is canted in the slightest, you will see it @ 500 yards.  When you get beyond 300 yards you will find that your ability to read the wind is FAR more important than a drop chart.

Edited by CWPINST - May/03/2008 at 21:49
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/04/2008 at 08:46
Dale Clifford View Drop Down
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its like shooting trap= every target has an angle, even if it is straight away -- long range shooting -- the wind is always blowing just a questionof how much.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/05/2008 at 06:44
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Yep. (I shoot a lot of trap too).
 
This is why I said you need a lot of REAL data, and cannot just shoot ten rounds, average POI and speed and plug that into an on-line ballistics calculator. It really is NOT that simple, but many people do it.
 
I think this would create a GENERAL GUIDELINE to get going with, but it is absolutely not a replacement for actual trigger time. Learning your ammo and rifle will gain you the best chance for success.
 
I was just on the Dwyer web site the other day and you can get the same wind gage the military operators use for $22.00... Get one, and learn to 'feel' the wind it indicates. Of course, this does not help you at range, but for $22.00 you can place one at every range and factor your wind with accuracy that is unavailable in the real world...
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