Cant get rifle to track using FFS!?

[Rabbitz]

Hey guys,

I am at a serious loss as to why my FFS program and my rifle wont mate up on the trajectories. I'm shooting at 1000yds. or less and it is consistently about a MOA high at almost every distance after 400 yards. I am fairly new to Field Firing Solutions, so maybe it is just something I am overlooking. I have chrono'd the rifle, checked the calibration of the scope, and reconfirmed my zero at 100 yards. On this particular rifle I am using a Leupold Mk. 4 with .25 MOA clicks and it is calibrated at . 249 MOA clicks at 100yds, which is damn good for a Mk 4 IMHO. At lets say 466 yds. for instance my FFS program is saying 10.8 MOA hold, but I'm finding its actually more like 9.8 MOA. Is there anything I'm over looking, or do I need to adjust something to make them meet? The only thing I can think of is that I need to calculate my BC myself. Are Berger's BC's that far off typically? Here is the data I'm using:

Rifle-

PCR built .308
22" Rock Creek m40 1-10" twist

Load-

Berger .30 Cal. 185 grain Match VLD
BC G1 - 0.549
Length of bullet- 1.378
Muzzle Velocity- 2525 fps.

Atmosphere-

Alt.- 1050
Pressure in Hg. - 29.53
Air temp- 59 deg.
Humidity- 66%

Any advice is going to appreciated. It isn't a huge deal that it's off consistently 1 MOA, it's not hard to adjust for, but I'd like to figure it out for my own knowledge what the hell is causing it.

Thanks

 

[Lowlight]

Adjust the numbers to true it,

Factory BCs are barely correct, they are a starting point not a statement of fact.

There are a lot of variables beyond your control, 1MOA as a starting point is fine, it's a starting point nothing more.

You can adjust the DK factor (that's what it's there for) just a tiny amount. The Muzzle velocity can be off via your Chronograph, add 40fps and see... You have to modify it to match your rifle, load and style of shooting.

 

[Graham]

Have you calibrated your Kestrel to use station pressure, and set the altitude window at zero in FFS?

 

[OutlawTen5]

You need to use the "Tools" function to True MV & BC plus make sure your atmospheric conditions are entered correctly as well as info on the rifle including sight height/above bore.

 

[Papa Zero Three]

Is your sight over bore height correct, as in you measured it? If so, look at your MV and BC.From the FFS website:


Verifying Muzzle Velocity using the POI Method - Using the chronograph muzzle velocity and the calculated ballistic coefficient, set up a target at around 400, 500 or 600 yards/meters, adjust the scope for the range of choice and fire five (5) carefully aimed shots. Measure the point-of-impact distance above or below the point-of-aim, use the workspace in the program (Delta III SD and above; see "POI Method - Muzzle Velocity in the Field" in the manual) and compute the muzzle velocity as shown by the actual impact points on the target. Depending upon how well the user shoots and how small the resulting group is, this is an extremely accurate way to determine muzzle velocity. Once the actual muzzle velocity is known, first update the bullet profile with this known muzzle velocity. Then, use the original muzzle velocity obtained from the chronograph and divide by the POI Method muzzle velocity. This will give you an error factor. Use that error factor to modify the down range velocity obtained from the chronograph and that will give the actual down range velocity. Using these two corrected velocities, compute the ballistic coefficient again. (It is assumed here that whatever error existed when using the chronograph near the muzzle, that same error will be present at the down range target. It is important, therefore, that the two measurements be taken at near the same time and under the same conditions to maximize the chances that this is true.)

Using this newly calculated ballistic coefficient, run through the process again: if the turret solution remains unchanged, assume the same POI distance on the target and recalculate the muzzle velocity, get an error factor, using the error factor compute the down range velocity and using these two velocities calculate the BC for the bullet. It should be very close to the previous result. If the scope setting did change, then adjust the scope and fire five (5) more carefully aimed rounds at the target, measure the POI versus POA distance and recompute the muzzle velocity, then proceed with obtaining an error factor, apply the factor to the down range velocity and recompute the BC. At some point this iterative process will produce no meaningful change in velocity and BC at which point the user can be very sure that he has a correct muzzle velocity for that load/bullet/temperature and a BC that will produce optimum down range elevation and windage calculations well into the subsonic region.

Someone may well ask why it is necessary to go through all this work just to use the program. The answer is that it isn’t. But it must be understood that the program will assume the accuracy of all data that is input and based upon that data will provide a firing solution. If the input data is erroneous, the resulting firing solution will be erroneous. In order to discover the errors in the measuring devices that shooters depend upon, it is necessary to check them and to make allowances for their inaccuracies when detected. There really are no shortcuts in this regard.

Videos:
MV

[video]http://www.screencast.com/t/vRjbE0iA[/video]


BC

[video]http://www.screencast.com/t/UO06y5wOkVn[/video]

 

[Rabbitz]

Thanks for the quick replies I'll mess with it a bit more tomorrow and see if I can verify the muzzle velocity. I figured it would need some fine tuning, i'll give it a go.

 

[Ring]

if u can, post your REAL dope for 300 600, 800, 1000

 

[Rabbitz]

if u can, post your REAL dope for 300 600, 800, 1000

I'll do my best I'll be going to a range tonight that has a max of 600, but I should be able to verify at 1000 Friday. I'll post back when I figure it out.