Data not matching up to what I see in the field. Thoughts?

[sharp360shooter9]

I’m running a Vudoo with a 16” mtu barrel with SK rifle match ammo that has always worked well for me with a Vortex AMG on top. The magneto speed v3 says I’m running 1068 with a SD of 12.5 after 10 shots. I live in South Dakota and during the summer my data reads true on my kestrel to what I see in the field to 275 but at 450 yards I have to add 2 mil and I can hit the 12” most of the time. I do have a 20" vertical spread at 450 yards with this set up.

Here is my problem. I go to shoot last night and is 42 degrees with a 8mph wind from 9 o’clock. I shoot at 50 to make sure my zero is good and I’m hitting the little .25” stickers no problem. I check at 100 yards and the kestrel says 2.0. I shoot and it’s a tenth high. So I change the MV just a little to make it read 1.9. So now I’m good there. I have 190 and 275 yards set up so I shoot at them. The kestrel says 6.3 for the 190 yard targets. After a few shots i find that I am hitting the 2” target at 190 with a 6.9 elevation. So I calibrate my MV in my kestrel to match what I’m seeing in the field. I check my 100 yard data and now it shows 2.0 again so I change my BC down to .150 to make 190 and 100 yard data match to what I see in the field. I go to shoot 275 yards and it calls for 12.3 and 1.3L. I shoot, no call. I figure wind, It’s always wind. After 3 more shots I find that wind was on but to get center impact I need 12.9 elevation. I go back to my data and change BC. Well now my other ranges are not right. I change MV still can’t get other ranges to match up. I can not find any combination of BC and MV that reads to what I see out in the field. I tried from .120-.178 for BC and 998-1100 MV and no luck. What do you guys think is going on?
Thanks for reading my mess of thoughts and feel free to ask questions.

 

[littlepod]

If you're not using custom curves, generally .135-.145 BC is what I've seen for SK ammo. Velocity is whatever is measured. Atmospherics makes a pretty big difference. So when you ran your Kestrel last night using the old BC the data should change with the atmospherics.

Velocity could also change quite a bit from summer to 40 degree weather, depending on if your ammo is just sitting out in the cold.

And then testing impacts at 190 / 100, unless you're certain that it's really 1.9 or 6.9 like doing 10 shot groups on paper and precisely measuring it, trying to true your data to rough approximations isn't good.

 

[sharp360shooter9]

My kestrel was on live environmental and I was running data that had proved to be true earlier in the year and that is when it was giving me 6.3 for 190. For my group I usually send 5-10 rounds down range to make sure I don't have a flyer or anything.

 

[usafa77]

I had good success using DSF as described by dtomas in another thread. Never have touched the mv or bc. Using MV on my centerfires seems to do the trick, but not here.

 

[Near miss]

Take notes on paper of:
-atmospherics
-bullet drop at various distances
-muzzle velocity

Then input the enviromentals from dope to Kestrel and create a new profile:
1) With CDM and adjust DSF (Elite)
2) With G1 and adjust BC (non-Elite)
..and adjust these, until it matches your drop data.

The problem with BC matching is that at 450 there might not be a BC number that will agree with your drop data. Try to get within 0.2 to 0.1, it should be enough for most.


-Please also make sure the groups you shoot at different distances reflect the MV.

If you input 1050fps to Kestrel and by a freak luck your 5 shots leave at 1020fps, you have corrupt data that will *really* mess with you.

 

[Gleedus]

You typically will not get it to match the curve perfectly using a G1 bc. To have it right at 400 yards you will need to have it set to show more elevation then is actually required at 200.
You probably with find with AB that running a G7 BC will be a closer match to the actual trajectory. The most accurate is normally going to be to use a custom drag model.
If using a BC i normally true 200 yards to call for 0.1 mil more then actual. Then its close out to 400.
Temp variation i use the fps per degree to true that i start with actual but you might have to adjust more or less the actual velocity difference. Expecially if using BC.

 

[junkyard.brody]

Make sure your bore height is correct. I had that issue before where I input my scope ring height. Measure from the center of your barrel to the center of your scope. It's a little detail that makes a lot of difference.

 

[Tim7139]

It might pay to remember any head/tail wind, even a modest quartering wind somewhere down range will give you a vertical component, sometimes a lot.