Trajectory question

[Bristleback]

I've thought and thought this over.........and decided to ask the experts.

I currently don't have a place to shoot over 200 yards with wind protection.

Given my load data, actual chronographed MV.........I decided to shoot at 200 yards..........then turn up my elevation UPto: and shoot from 200 yards and take measurement readings:
300 yards
400 yards
500 yards
600 yards

.........now if I take these hits at 300-600 and measure UP from my zero.............will they EQUAL my "projected trajectory".........at the given distances.
Another way of asking: will the distance ABOVE ZERO equal the same amount of FALL from my ZERO.

Example: 200 yard zero: ballistics graph says @ 300 yards I'll be -4.3"...........I measure -1.5"(difference of almost 3")
@ 400 it says I'll be -13.3........I measure -7.5" (difference of over 6")

..........please set me straight, I've given this a lot of thought and thinking the measurements will NOT be the, initially I thought they would/should be.........or at least very close?
Thank you.

 

[brian427cobra]

I suggest you stop thinking in inches feet yards and start thinking what angle of measurement do I need to dial into my scope to hit my target, and learning to read the wind is very important to long range shooting, chances are your scope adjusts in MOA(minutes of angle), don't cunfuse the 1/4 moa with 1/4 of an inch, there close, but not exactly the same, I use a 100 yard zero, my come up for my 308 at 1000 yards is 36.2moa(175 smk 2700fps) no where does how many inches of drop come into the picture, BTW its 372 inches, thats useless information because scopes don't adjust in inches.

Using ballastic calculators has flaws, and those flaws all come from the information we feed it, garbage in garbage out, http://www.jbmballistics.com/ballistics/calculators/calculators.shtml is what use, find your bullet, tell the program all the information it asks for(scope hieght, temps, altitude, baro, fps, angles), set the out put to what ever unit of measurement your scope adjusts, then verify the out of JBM by shooting, if all your inputs are correct, the output will dam close if not exact.

 

[MrMajestic]

BB, I have read that 3 times and still not sure I understand! If you mean that your drop from 200 is -13.3 at 400 would you be +13.3 at 200 for a 400 zero, No. Go to the JBM website and plug in your numbers and you should get the information your looking for.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
You can not guess at your trajectory because of all the variables. You must shoot at distance to be sure and then you change altitude, temperature, barometric pressure, actual BC etc. and it all goes out the window! Good luck.

 

[Bristleback]

Many thanks for the replys.......I appreciate it.

Yes, I'm using the JBM calculations.

Using actual MV and all the variables I know, no guessing.

Yes, my question was would my point of impact OVER my zero, be the same as my point of impact BELOW zero.....at the given yardage.
The range I'm at is a max 200 yard range:
200 yard ZEROI have a turret, dial it up to 300 yards......... and shoot it at 200 yards.......measure the POI above my ZERO 200 yards........

All shots were taken at 200 yards.......turn my turret to 300, 400, 500, 600........each shot is HIGHER than the previous ABOVE my zero........I was asking if my DROP below zero would be the same as the amount above my zero............just wanting to verify my turret..........until I can actually shoot at 300-400-500-600.

 

[Nomad47]

brian427cobra, I must respectfully disagree.....on two counts. Some scopes do adjust in inches per 100 yards. Sightron for example was in inches until early this year.
And you can obtain scope correction from drop. Even MOA correction from inches of drop. To convert inches to MOA, multiply by .9549 . 1000 yards is easy since it is ten 100s. You said your drop at 1000 was 372". So scope correction in inches is 1/10 or 37.2". And in MOA it is 37.2 times .9549 which is 35.5 MOA.

 

[brian427cobra]

Using math is fun, but its also confusing to people who need simple answers to longrange questions, I tweeked JBM match my actual DOPE from June of this year, it spit out 372 inches, its still useless information IMHO. I have only seen US Optics IPHY scopes, good to know that other companies make IPHY, I'll stick to MRADs, its a dead simple system that has no value unless the user assigns one, 1 MRAD is 1 1/1000 of any unit of measurement in the world, on my 308 I use a MOA MOA scope, shooting FTR is a static position shooting sport, SFP MOA scopes like my Nightforce are perfect for that, but I don't shoot much FTR anymore, a different tool is required for Sniper matches where shooting at varying distances with out time to dial is needed, FFP Mil Mil like my Premier Reticle is needed, different tools for different jobs. Bristleback I suggest you find someone who trains shooters on whatever kind of shooting your interested in, education is the one thing that can never be taken away from you.

 

[Rem06]

Another way of asking: will the distance ABOVE ZERO equal the same amount of FALL from my ZERO.

i think i see the real question? (regardless of units used)

you can only shoot 200yds. if your chart reads "with a 200yd zero you should be say 11" low at 500yds"

question is :
"will you be 11" HIGH at 200yds"?

or (replace inches with MOA or MILLS)
is that correct
Bristleback

you want to know if you can measure your far drops by measuring height above sight at your 200yd zero?

nope.

 

[Bristleback]

Thanks everyone, I appreciate the help.

 

[necchi]

The range I'm at is a max 200 yard range:
I was asking if my DROP below zero would be the same as the amount above my zero........

No.
Using the Point Blank progam(or any), to see the proper change at 200 for a 400 yard zero,, simply change the "zero distance" on the program too 400 (or 300-400-500-600-700).

I don't have your data, but entering random (close approx) to what you should have to get -13.3 at 400 for a 200yrd zero,,
I change the "zero" too 400, click "Compute Ballisitcs" again, and get +6.72 at 200
(again random data--not yours)
You just have to keep changing the info in the "Zero Distance" box to see what the change at 200 will be.
Get it?

 

[swt5]

Reading the replies by Rem06 and necchi finally cleared up the picture on the original question for me. Sorry, I guess I'm slow
If the particular ballistics program you are using advises a certain number of "come up clicks" at 500 yards with a 200 yard zero, your subsequent 200 yard group will not print high the same as the drop in inches advised for 500 yards because MOA's are not the same at different distances (measured in a linear fashion anyways) and the actual trajectory of the bullet is an arc and not a straight line. If shooting at 200 yards and your come ups are "X" number of clicks to be zeroed at 1000 yards, figure out what "X" equals at 200, not 1000.
In addition, as stated by others here, I've found ballistics calculators just get you in the ballpark and you need to actually get out there and shoot groups to confirm/adjust your numbers.