Is there a scope adjustment calculator?

crzybowhntr

New member
I am going to be shooting in a varmint shoot from 100-500yds in a few months and would like to know if there is a way to get a rough idea of needed adjustments in order to be near or on target from different distances before I go waste a lot of ammo and try for myself. I know I can do it based off of ballistics but not too sure I know exactly how to read them correctly. If it matters I am shooting a 55grn Hornady sp and spsx with either 24.5 grns of Benchmark or 24.3 of IMR 4895.
 
It's built into RSI shooting software. You enter your scope click values in
your rifle info and the program uses it in the exterior ballistics and the target
sections automatically.
 
If you can use a chronograph to crack off even a couple of rounds thru it would help immensely. With a known bullet, known speed and any basic ballistic info (whether it be software or even a good loading book) you can get very close.
 
sure, all it is is an estimate of the bullets path, this info will get you close.
muzzle velocity, published bullets BC, heighth of the center of scope above center of bore, and the exact barometric pressure where you are hunting/shooting.
Now you need a rangefinder, a repeatable scope and a drop chart of some sorts.
Here is what I carry in the field
leica 1200 LRF
pda loaded with exbal (ballistic program)
kestrel 2500 (b/p, temp, alt) if you know bar pressure, alt. is a moot point.
level on the scope
an angle finder (for uphill downhill shots)
a rear support (I use a foam cushion)
so you end up with something like this
LRrigs.jpg

Now practice, see where your hitting compared to the ballistic program readings, most of the time you have to tune your chart to your rifle, if you know b/p, muzzle velocity, scope height, the only thing you haven't measured yourself is bullet BC, so how do you fix it?
First shoot at 300,400,500 yards measure your actual drops, are you hi or low? most probably from my experience you'll be high.
This tells you your not dropping as much as your chart says you will, so if like I said before everything is correct, it has to be the wrong BC, so slowly raise the bc of your bullet in your program until your drops match the chart BINGO! now if your on at 300, 400, 500 yards, it just stands to reason you'll be on at 700, 800 and 900 yards.
Once you understand how it works, this isn't that diffacult.
1350.jpg

RR
 
Dang thing is shorter than the rifle. Should fit in your cooler nicely......... /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/grin.gif
 
Quote:
Dang thing is shorter than the rifle. Should fit in your cooler nicely......... /ubbthreads/images/graemlins/tongue.gif /ubbthreads/images/graemlins/grin.gif


its a mature doe (90-100 #), the rifle is 53" long.
RR
 
We call those "crock pot deer" here........ /ubbthreads/images/graemlins/grinning-smiley-006.gif

Just messin' with ya...........
 
Quote:
This tells you your not dropping as much as your chart says you will, so if like I said before everything is correct, it has to be the wrong BC, so slowly raise the bc of your bullet in your program until your drops match the chart BINGO! now if your on at 300, 400, 500 yards, it just stands to reason you'll be on at 700, 800 and 900 yards.
Once you understand how it works, this isn't that diffacult.



If you are using ESKIMO or the like, that is the way to get a true drop....

BUT, if you are using the EXBAL program, in lieu of messing with the b.c. directly, you can use the TRAJECTORY VALIDATION feature in the OPTIONS tab. It tweeks the bullet's velocity to make your #s crunch, in lieu of skewing b.c. Same difference to me, as long as my raw & actual data match!

The TRAJECTORY VALIDATION feature in EXBAL allows you to quickly correct your hits by inputting the height difference of your actual hits at a known distance, as compared to the data given for your present conditions. It is so easy to do that it took me longer to type this post than it would have to corrected a complete drop chart (minus the shooting part) /ubbthreads/images/graemlins/grinning-smiley-003.gif
 
it may work at times, but! if you chrony your load, and then change the MV to make your drops come out right, your windage adjustments will still be off due to the published BC being incorrect for your conditions. BC always outruns velocity at long range.

I put in my actual cold bore muzzle velocity, and work the BC from that, the published BC is what the makers got at the velocity they checked them at, at the BP they checked them at and some makers correct for sea level. of all the bullets I have tested the only bullet that the published BC matched my actual BC was the lapua 139 gr scenar, and it ain't worth a darn to hunt with. shoots awesome but performance is terrible.
RR
 
Ridge, I posted that up knowing that you use EXBAL and assuming you were familiar with that option of the program. I was explaining that feature to other members who may not be as versed in the program's useful tools...

I'm by no means a ballistic engineer, but I know that the b.c. of a projectile changes slightly as velocity bleeds off with distance. So either way, skewing b.c. OR velocity is just a means to an end...that end being getting your real world drops to match the EXBAL's theorized drops, based on the data you gave the program...

Its easy as cake to use the Trajectory Validation feature in EXBAL. If I'm shooting 4" high @ 600yds, I click the option, type 600 in the RANGE tab and 4.0 in the ELEVATION tab and viola, a new drop table is calculated when I hit APPLY. It just takes the guesswork out of picking the "correct" b.c. to get all your data to jive as efficiently as possible...

I wasn't disagreeing with ya /ubbthreads/images/graemlins/grinning-smiley-003.gif
 
I see what your saying but lets run some numbers

My 7mm load is as follows
160 nosler accubond at 3575 fps, its a proven load, have taken deer to 1350 yards with it.
Nosler publishes the BC at .531, the first year and a half I always was shooting high till I ran some tests, found out my actual BC for this bullet is .62.
This load sighted in at 300 yards is -80.32" at 800 yardsat
At this velocity with the BC at .531 it says its -83.6" at 800, I know this is 3" high at that range at that BC setting.

So lets say I leave the BC at .531 and jack the MV up to 3637 so its -80.33 at 800 the up and down will match up for a ways, but lets say I have a 10 mph wind. wind drift with the 3637 fps .531 BC at 800 is 41", but the wind drift at 3575 fps/.62 BC is 34.7" at the same range, so holding dead on a deers shoulder at 800 yards with the BC left at .531, and the MV moved up to make zero, you've missed before you even shot. make sense?
RR
 
Certainly does, but gravity is a constant value that can be calculated for...

Wind, on the other hand is never the same and simply cannot be quantified accurately over any appreciable distance, especially @ 800yds in the field on a deer. Sure Kestrel can get you accurate wind data at your muzzle, but what about the rest of the way? Guessing that is voodoo magic, my friend...

I'd be more apt to believe that my chrono were reading consistently slow and I misjudged the wind call than I would the other way around. The only way to test your dervied b.c. in the wind scientifically would be to artificially produce that wind velocity accurately for those entire 800yds at a given angle and see how far that bullet sails off course...

So consider your data above again. You make a wind call at the muzzle of 10mph, but it actually averages 7 mph over those 800yds, due to terrain & gust variables. That minute misjudgement would net you the same miss due to the wind call...

Calculating drop is easy.

Calling wind is voodoo magic...
 
thats just it, what a program does is artificially produce wind, if everything is right, and you set for your kestrel reading and miss, then you guessed wrong, so if you missed before you shot in a steady 10 mph wind, what happens is a variable one?
thats my thing, get everything I can control as close to being right as I can and better results will be obtained. but if your off 6" before you shoot whats the best you can expect?
the majority of my LR deer shots involve 16-30" of windage adjustment, when your waiting for the shot, take note of the amount the grass or limbs are blowing in relation to what they are doing at your position, with practice it comes around, had one bad hit from a wind call, missed POA by about 6", it was still a bang/flop from 600 yards.
RR
 
I understand the necessity for being precise in the long range game. But how do you know if you missed before you even shot? It sounds good, but it can't be proven it scientifically, based on the premise that wind is NOT a constant value...

The b.c. of a bullet can't be calculated via a wind call, especially one at 800yds! You simply cannot scientifically prove that it is in fact a 'constant' wind throughout that distance. So justifying a b.c. modification to account for a wind value that can't be accurately measured to the required tolerances under field conditions just doesn't sit well with me...

I'm positive that I'm not near as good a wind reader as you, or as experienced a long range shooter as you, Ridge. And I know that manufacturer's b.c. data is to be taken with a grain of salt. Not sure which use the G1 model accurately or are just trying to market their product as being 'better' than the rest. Who knows...

That said, the technique to modify drop tables I made note of above was learned from 'Mr. 338 Edge', Shawn Carlock. That's how he makes & modifies his drop tables, and I have subscribed to it, since it just makes too much sense to me. EXBAL makes the task easy to do and it is proven to provide desired results, so who am I to question it?

Back full circle. As long as your system works for you to make your shot, then that's the right way to get it done...

Tastes great,
LESS FILLING...

good shootin' /ubbthreads/images/graemlins/grinning-smiley-003.gif
 
Ridge or Knockem?

I don't shoot past 6! One thing that does (intrigue) or confuse me is, when you load data into exbal. How do you determine center heigth of scope when its sitting on (whatever 10,20,40 MOA) bases?

Now I'm not a rocket scientist by any means!! But as a machinist I do know that it is a heck of a lot easier to determine the heigth of scope when it's sitting level to barrel than when sitting at angle to barrel (on MOA bases), with undetermined differences in ring heigths!

Even different ring heights change everything (POI) when angles come to play! Help I'm confused!! /ubbthreads/images/graemlins/smiliesmack.gif /ubbthreads/images/graemlins/laugh.gif
 
That is some impressive shooting. I haven't got much experience with that. My longest shot was an elk at 560. And I misjudged the windage about a foot.

I was just going to say that what works in WV probably won't work as well in SD, as we actually have wind here. Can you tell the difference between 22 mph and 20 mph?

Not that you can't do it here, just have to be very patient waiting for conditions.
 
Speed,
The cant of a 20MOA base will have a negligable effect on the scope's height above bore. For a goof, change the scope height data in EXBAL by .1" and see how much it affects your drop at 600yds and you'll see for yourself...

Just measure the center of your scope's main tube to the center of your barrel. If you have horizontally split rings, measuring from the the split in the rings to the center of your barrel . A ruler works fine, or use your calipars /ubbthreads/images/graemlins/grinning-smiley-003.gif If it makes you feel better, you can measure in both the front and rear, then input the average...
 
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