ballistics info please

[chet]

ok, so I just got a new scope, Cabelas Alskan guide w/rangefinder....
now it's not the 18" circles I care about, it's the aiming points..... and the impact point are as follow:

200yd=zero
300yd=8"
400yd=23"
500yd=44"

now that sounds all well and dandy..... but how close is this going to match up to my rifle?

here's my info:
cal: .257 wt: 110gr bc: .420 mv: 3150fps

please enlighten me........ my initial thoughts are that the rifle is too flat for the scope.......

 

[FOTIS]

OK go to

http://www.eskimo.com/~jbm/calculations ... tions.html

plug in the values to get a general idea. You "should" shoot to those ranges to verify drop. Also remember that your trajectory does not have to be dead on with this. It can ba, and most likely will be +/- 2inches at each range.

 

[FOTIS]

Trajectory (Basic) Output
Input Data
Ballistic Coefficient: 0.420 G1 Bullet Weight: 110.00 gr
Diameter: 0.308 in

Muzzle Velocity: 3150.0 ft/s

Sight Height: 1.50 in LOS Angle: 0.0 deg
Cant Angle: 0.0 deg

Wind Speed: 10.0 mph Target Speed: 10.0 mph

Temperature: 59.0 °F Pressure: 29.92 in Hg
Relative Humidity: 0.0 % Altitude: 0 ft

Std. Atmosphere at Altitude: No Corrected Pressure: Yes
Target Relative Drops: No Zero at Max. Point Blank Range: No
Calculated Parameters
Elevation: 3.19 MOA Azimuth: 0.00 MOA

Atmospheric Density: 0.07647 lbs/ft³ Speed of Sound: 1116.5 ft/s

Maximum PBR: 372 yds Maximum PBR Zero: 317 yds
Range at Max Height: 176 yds Energy at PBR: 1321.3 ft•lbs

Sectional Density: 0.166 lbs/in²

Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yds) (in) (moa) (in) (moa) (ft/s) (none) (ft•lbs) (s) (in) (moa)
0 - 1.5 *** 0.0 *** 3150.0 2.821 2423.2 0.000 0.0 ***
100 -0.0 -0.0 0.7 0.6 2912.7 2.609 2071.8 0.099 17.4 16.6
200 -2.6 - 1.2 2.8 1.3 2687.8 2.407 1764.2 0.206 36.3 17.3
300 -10.0 -3.2 6.5 2.1 2473.9 2.216 1494.5 0.323 56.8 18.1
400 - 23.2 -5.5 12.0 2.9 2269.9 2.033 1258.3 0.449 79.1 18.9
500 -43.0 -8.2 19.6 3.7 2075.5 1.859 1052.0 0.587 103.4 19.7

 

[FOTIS]

Now the above is at sea level. If you were 6K+ feet as I am it would be nowhere near your scopes circles.

 

[chet]

ok, so if I zero it dead on at 100yds:

200 = -2.6"
300 = -9.9"
400 = -22.5"
500 = -41.2"

as compared to:

200 = 0"
300 = -8"
400 = -23"
500 = -44"

zeroing the rifle at 200 makes the scale useless, but zeroing at 100 makes it very close....... I entered 3100fps, it may be more realistic. also I entered 6000 feet above sea level. guess I'll mount it up and try it out!!!

 

[FOTIS]

Chet:

Now do not despair! There are many ways to use that scale. Try sighting it in at 90 or 95 or 135 yards (you get my drift). You might get closer to the scale. That is what I do with my Burris Ballistic plex because I do live in Cheyenne WY and hunt elk at 7-10K feet altitude. Remember you want the biggest fluctuation at short range not long. 4" for instance at 100 yards on an elk is nothing!

 

[chet]

ok pop: so what if I sight in the 500 yd hair at 500 yards..... then just see where it hits at the other marks??? good idea, bad idea????
I mean after all it's gonna take alot of practice no matter what.......... I'm just gonna bolt it down and shoot the sunabitch

 

[Accubond Believer]

Even Burris will say that with the ballistic plex sight the 400 or 500 yard bar in first and then check your closer distances to see if you are hitting high or low. Another point to think about if you are at longer distances have the variable scope turned all the way up. some scopes adjust point of impact with what power the scope is set on.

Just my two cents.
Steve D. the HP

 

[chet]

thanks for bringing that up AB! the leopolds are easy cuz you can fine tune your POI with the power ring.... but this particular scope has the reticle on the magnification lens so it enlarges with magnification..... so, hopefully everything stays in line with power increases. My rings and bases should show up today and I will check everything out on the collumnater asap to be sure of this...... If all seems well I beleive I will zero at 400 yards first, then see where the other ranges hit!

thanks guys, and sorry for my spelling, gramer, puncctuation, and terminology.........

 

[FOTIS]

ok pop: so what if I sight in the 500 yd hair at 500 yards..... then just see where it hits at the other marks??? good idea, bad idea????
I mean after all it's gonna take alot of practice no matter what.......... I'm just gonna bolt it down and shoot the sunabitch

That would work, unless the point of impact varies too much at closer ranges; where you have to remember too many variables at different ranges... I usually sight in where I only have to worry about one specific range and all others are +/- 3-4" off center.

for instance....

Load you quoted but at my 6000 feet sight in at 100 yds

Range Drop reticule drop variation form actual
(yds) (in)
100 -0.0 1.5 1.5
200 -2.5 0.0 2.5
300 -9.5 -8.0 1.5
400 -21.6 -23.0 1.4
500 -39.6 -44 4.4

Now, given the above I can live with the variations at different ranges. If you plugged in the Burris Ballistic plex values....believe me you would be way off in some ranges. I palyed with the above example and for my rifle and the Burris my best zeroing range was like 180 yards for small variation at the different ranges.


Load you quoted but at my 6000 feet sight in at 200 yds

Range Drop reticule drop variation form actual
(yds) (in)
100 1.2 -1.5 1.5
200 -0 0.0 2.5
300 -5.8 -8.0 1.5
400 -16.7 -23 5.3
500 -33.5 -44 4.4


Look at both scales and see the less variance between the 2 and choose the lesser one.
Hopefully I did not confuse you.!