Can someone run some data for me to QC a chrono?

[flyingfisherman]

How do guys,

 

Finally got a load worked up for my new shooter. Got a speed for it, using a 15 round average and also checked the drops to 300m. Now the drops don't correlate to what the calculator (Ballistic AE) says with the speed that ive used. My chrono is a chrony and im always skeptical about chronographs. So much so that i generally just go get drops rather than trying to fiddle a BDC in an app. I'd be interested if someone else can run the bit of data ive got and see what speed it comes out with. Apologies that the data only goes out to 300m, i didnt have time to get out any further.

 

Bullet: Hornady AMax .264 140gn

Avg. Speed: 2797fps

 

Zero Range: 91m

Chrono Distance: 10'

QFE: 1013

Temp: +15C

 

Actual drops (3 shot groups used)

 

200m -3.7''

250m -7.75''

300m -12.75''

 

All groups were consistent with the accuracy of the gun, so believe them to be repeatable.

 

What i'd like to know is what speed people think the above bullet needs to go to achieve the drops above, using the data provided..

 

AND... What the drop should be at 450m.. Ive got a gong out at that and will give it a whirl tomorrow.

[Deserttech Europe]

Hope this is of some help

 

The untitled column is the relevant one (path in inches).

 

Ewen

 

CB1_Ballistics_Results_2.pdf

[triggersqueezer]

notice you have not put scope hight in there and that affects things ?ballistic ae if a swine you can't just amend data at the hub you need to imput a whole new data, calculate drops then re add to favorites each time or it picks up old data.i tried to run it through but mine works in yards i'm sure in settings i can change it but i'm off out shooting but with a scope hight of 2.2

 

220 yds - 3.92

270 yds - 7.96

330 yds - 14.88

i'm converting to yards and rounding up but its not far off .a tweak with scope hight or fps should get you bob on.

good luck

 

silly question but was it totally flat when you got your real world data as cosine angle has a dramatic affect.

[flyingfisherman]

The scope height is about 1.6'', which i forgot to mention was inputted into B-AE. Regarding angle, its pretty flat.. certainly would class it as a flat field (apart from where the target was, in front of a huge bank).

 

Was more just querying my speed really. The only way i can get the calculator to match the actual drops is to look up the range in yards on B-AE which gives me the drop in metres (real world).. Ive checked the settings in the app and am metres/mils on all...?

[Brummy Mark]

Hi, I note that your barometric and temp listed in your post, as well as the distance from the muzzle to chrono match the default settings that ballistic ae gives when you first set up new bullet etc.

What was your actual station temp, baro, altitude and humidity,what was the actual distance from the muzzle of the chrono?

 

You need to put that in to bae first then ' true up the data', if you leave at default then ballistic ae gives a muzzle speed of 3030fps:

200m -3.70 inches

250m --7.71 inches

 

After this the drops predicted by bae are increasingly off ie

300m -13.31 inches instead of your actual measure drop of 12.75 inches.

 

Now, me personally using ballistic ae for shooting out to 900 yds and getting consistent 1 st round 0.5 to 1.5 moa hits out to 800yds from the drops predicted by ballistic ae gives me confidence in this app, also me having lots of actual drop data at various ranges and conditions, all entered to true up BAE makes it even more accurate.

 

This logically leads me to sum up: some of the data you have put in your post does not stack up mathematically, for example to get the 12.75 inches of drop at 300m your MV would have to be 3080fps, but this would mean your 200m drop would be -3.5 inches and your 250m drop would be -7.36 inches.

Somthis means your mv would be somehwere between 3030 and 3080 fps for it to match.

 

So this means either your chrono is out by 200ish fps, perhaps the chrono is at fault, or your accuracy of measuring your average drop needs tweaking, after all once your MV is raised to make the drops match, we are only talking about 1/4 inch between your measured drop and the predicted drop, shooter error can induce more than that, justp the slightest bit of wind can shift.

 

Borrow a chrono and check again as BAE works extremely well when you give it the right data.

[Bianchi]

Would tend to agree with Brummy w.r.t. the chrono. I regularly use JBM Ballistics and ran Flyingfisherman's data with it as a check. JBM suggests approximately 3040 fps which correlates reasonably well with the actual drops observed from 200 to 300m.

 

Key inputs and results follow. Some assumptions regarding barrel twist, humidity and altitude were made.

 

Input Data

Manufacturer: Hornady Description: A-Max® (Litz)

Caliber: 0.264 in Weight: 140.0 gr

Ballistic Coefficient: 0.299 G7 (ICAO)

 

Muzzle Velocity: 3040.0 ft/s Distance to Chronograph: 10.0 ft

Sight Height: 1.60 in Sight Offset: 0.00 in

Barrel Twist: 8.0 in Twist Direction: Right

 

Temperature: 15.0 °C Pressure: 1013.00 mb

Humidity: 50 % Altitude: 150.0 m

 

Output Data

Elevation: 3.380 MOA Windage: 0.000 MOA

 

Calculated Table

Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead

(m) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)

100 -0.1 -0.1 0.1 0.1 2872.0 2.572 2563.8 0.111 0.0 0.0

150 -1.1 -0.7 0.1 0.1 2787.2 2.496 2414.5 0.169 0.0 0.0

200 -3.6 -1.6 0.2 0.1 2703.5 2.422 2271.7 0.229 0.0 0.0

250 -7.4 -2.6 0.4 0.1 2621.2 2.348 2135.5 0.290 0.0 0.0

300 -12.8 -3.7 0.5 0.2 2540.3 2.275 2005.7 0.354 0.0 0.0

350 -19.7 -4.9 0.8 0.2 2460.7 2.204 1882.0 0.419 0.0 0.0

400 -28.4 -6.2 1.0 0.2 2382.6 2.134 1764.4 0.487 0.0 0.0

450 -38.9 -7.6 1.3 0.2 2305.9 2.065 1652.6 0.557 0.0 0.0

500 -51.4 -9.0 1.6 0.3 2230.7 1.998 1546.5 0.630 0.0 0.0

 

The calculated drop at 450m is 38.9". @Flyingfisherman: Did you manage to test at the gong and if so, what was the actual measured average drop?