Making bigger than expected adjustments on BC?

[regency]

Anyone ever had a load dialed in with velocity verified, then you go out shooting on a later date and all of the sudden you are having to artificially adjust your velocity or bc up or down by a large amount to line up with your impacts down range?

Example today, shooting my 6.5creed GAP rifle with 140 hybrids.

Today I had to adjust the BC down to .288 to get it to sync up where as a few months ago .312 was perfect. I was shooting at 900yds max. Velocity was only 5-7fps slower today on the Labradar.

*Using kestrel with AB

 

[seansmd]

You said you are using the kestrel with AB , assuming you captured live environmental data?

Any shimmer(mirage) on either day?

 

[_Windrider_]

Anyone ever had a load dialed in with velocity verified, then you go out shooting on a later date and all of the sudden you are having to artificially adjust your velocity or bc up or down by a large amount to line up with your impacts down range?

Example today, shooting my 6.5creed GAP rifle with 140 hybrids.

Today I had to adjust the BC down to .288 to get it to sync up where as a few months ago .312 was perfect. I was shooting at 900yds max. Velocity was only 5-7fps slower today on the Labradar.

*Using kestrel with AB

The BC tweaking is more a G1 thing rather than a G7 thing

 

[LawnMM]

Check your scope and make sure it's tracking correctly and repeatably

 

[AIAW]

That‘s a big BC change if you truly had good verified DOPE using the higher BC previously.

Sounds like environment to me also.

 

[regency]

The temps were cooler (and that was taken into account with the kestrel) but velocity was essentially the same, a little slower.

Mirage was a little worse than it usually is, thats about the only 2 things that seemed different about environment.

 

[Dthomas3523]

Factory ammo or loaded?

Which ammo or load specs?

Same lot of factory or same loT of bullet if loaded?

How confident were you in your previous data? Was it just one day worth of data from before or something like an entire season of shooting that load/bullet/ammo.

 

[regency]

Factory ammo or loaded?

Which ammo or load specs?

Same lot of factory or same loT of bullet if loaded?

How confident were you in your previous data? Was it just one day worth of data from before or something like an entire season of shooting that load/bullet/ammo.

Loaded ammo:

140 hybrid Berger doing about 2,760-2,780fps depending on temperature and this is the same lot. (Powder is H350 with alpha brass and cci primers, round is .010 off the lands)

I had been shooting this load for quite some time. On initial load, I had the G7 BC adjusted to 3.13 to make it perfect.

I did do the most recent update on my kestrel and I see it changed some of the saved settings I had. I'm trying to compare JBM ballistics with my kestrel at the moment. JBM looks closer to my range results from yesterday but still about .2mil off at 900yds

It took 7.1-7.2 mil of elevation to get consistent hits at 900 on a 100% ipsc target, kestrel is telling me 6.86mil

 

[Dthomas3523]

Loaded ammo:

140 hybrid Berger doing about 2,760-2,780fps depending on temperature and this is the same lot. (Powder is H350 with alpha brass and cci primers, round is .010 off the lands)

I had been shooting this load for quite some time. On initial load, I had the G7 BC adjusted to 3.13 to make it perfect.

I did do the most recent update on my kestrel and I see it changed some of the saved settings I had. I'm trying to compare JBM ballistics with my kestrel at the moment. JBM looks closer to my range results from yesterday but still about .2mil off at 900yds

It took 7.1-7.2 mil of elevation to get consistent hits at 900 on a 100% ipsc target, kestrel is telling me 6.86mil

And how many mil did you need before to get to 900yds when you were using .311?

 

[regency]

My bad, should have stated I was using the .311 all along, even when the ballistics were good prior.

I had to go down to .288 G7. One thing was weird after the update, my scope height was saying 2.75 when it should have been 2.25. Fixed that and the numbers look a little better, now it is saying 7.0 mil on the kestrel for 900yds (using .331 G7). Still need it to say 7.1-7.2

I'm checking environment settings right now, I'm not seeing anything that is off at the moment. The 900yds was verified with a Terrapin-X.

 

[Diver160651]

Did you check your zero and confirm you didn’t have a shooter offset before getting to worried about the re-tuning?

having a .1 shift in the shooter is not uncommon-

 

[regency]

Did you check your zero and confirm you didn’t have a shooter offset before getting to worried about the re-tuning?

having a .1 shift in the shooter is not uncommon-

It was hitting perfect and tight at 100yds.

 

[Dthomas3523]

Let me rephrase:

Were you using 7.1-7.2 mils at the time you are referring to when using .311?

Basically, did nothing change with your real world data and only in the calculator?

Or were you using less elevation before to get to 900yds?

 

[regency]

Let me rephrase:

Were you using 7.1-7.2 mils at the time you are referring to when using .311?

Yes.

Basically, did nothing change with your real world data and only in the calculator?

Outings in the past, the kestrel was spot on at every distance out to 1,200yds using the .311 and velocity provided by the Labradar

Or were you using less elevation before to get to 900yds?

Kestrel initially told me 6.9mil to 900yds and I was shooting the dirt below the target

 

[regency]

I think fixing the bore height after the update has me closer, and checking the Berger website just now, I see they have the G7 BC adjusted to .311 now and not the .317 it used to be.

 

[Dthomas3523]

I think fixing the bore height after the update has me closer, and checking the Berger website just now, I see they have the G7 BC adjusted to .311 now and not the .317 it used to be.

View attachment 7163274

This still doesn’t account for needing to go to .288 to get 7.1mil when you’re saying you used .312 to get 7.1mil in the past when the bore height didn’t get you back to where you needed.