Range Report Velocity Tweak?

[CarbonOne]

Working on dialing in my 260.

I'm using ballistic fte On the iPhone and "think" I'm getting the correct data input. I've chronod my loads, using g7 bc, updating the atmospheric conditions, etc...

Well, realworld shooting at 300, 500, and 800 yards using fte puts me way high. I thought maybe the scope adjustments were off, but I hit the same spot if I dial or holdover with the reticle. So I know it's not the scope.

If I increase my muzzle velocity in fte almost 200fps it starts to fall inline with where I'm actually hitting. I really like fte. I am surprised I'm off by almost 200fps.

Rather than plugging in a bogus fps should I be plugging in a bogus bc to get me inline with my realworld results?

Or any other suggestions? Thanks guys! If it'd be helpful I can give you the exact numbers.... I'm averaging about 2700fps with 140 Berger vlds and 142 Sierra matchkings a tad slower, and having to input 2900 fps to inline the fte drop.

 

[CarbonOne]

Re: Velocity Tweak?

How about tweaking the zero? Just wondering which variable is the best to mess with.

 

[rmfield]

Re: Velocity Tweak?

Barrel length? What load? What chronograph? Scope make/model? What is "way high"?

 

[BobinNC]

Re: Velocity Tweak?

I took your velocity data of 2700 FPS w/Berger 140 VLD and created this JBM table: I used Litz's G7, and computed drop in both Mils and MOA, not knowing which you used.

Trajectory (Simplified)
Input Data
Manufacturer: Berger Description: VLD (Litz)
Caliber: 0.264 in Weight: 140.0 gr
Muzzle Velocity: 2700.0 ft/s
Sight Height: 1.87 in Line Of Sight Angle: 0.0 deg
Cant Angle: 0.0 deg
Wind Speed: 10.0 mph Target Speed: 10.0 mph
Temperature: 92.0 °F Pressure: 30.01 in Hg
Humidity: 50.0 % Altitude: 200.0 ft
Std. Atmosphere at Altitude: No Pressure is Corrected: Yes
Zero at Max. Point Blank Range: No Target Relative Drops: Yes
Column 1 Units: 1.00 mil Column 2 Units: 1.00 MOA
Round Output to Whole Numbers: No
Output Data
Elevation: 4.146 MOA Windage: 0.000 MOA
Atmospheric Density: 0.07091 lb/ft³ Speed of Sound: 1151.5 ft/s
Maximum PBR: 342 yd Maximum PBR Zero: 290 yd
Range of Maximum Height: 161 yd Energy at Maximum PBR: 1569.6 ft•lbs
Sectional Density: 0.287 lb/in²

Range Drop Drop
(yd) (mil) (MOA)
0 *** ***
100 -0.0 -0.0
200 -0.5 -1.6
300 -1.2 -4.1
400 -2.0 -6.8
500 -2.9 -9.9
600 -3.9 -13.3
700 -4.9 -16.9
800 -6.1 -20.9
900 -7.4 -25.3
1000 -8.8 -30.1

So how does this compare with what you are generating from your program? Better, worse or the same, compared to your actual data?

I will note that many shooters are running 2850 FPS + with their 140 gr loads, so 2700 does seem a tad slow. What's your load and barrel length?

Bob