good chrono #s, use G7 on solver to adjust BC to true your dope?

[bojangles808]

I always wondered what you do if you get solid chrono numbers but when you go to true, you are off. I get a lot of the time its not a good 10 shot zero but if it is, and you are using AB and ELDMs then what? I thought I read on here a while ago not to adjust the g7 BC, but using AB these pro shooters seem to advocate for it. Which one is it, and what do you check off if your dope is off with solid chrono numbers? what kind of SDs make it an ammor problem?

 

[XLR]

99% of competitive shooters adjust BC to true their data. I wrote this a while back on trueing data if you would like to check it out.

Truing Rifle Data

This is the time of the year when shooters start getting the itch. It is the best time to start brushing up on your wind calls and making sure that your rifle is shooting well! One common question that we get asked is how we true our data when we gather dope. This is a great question because...

xlrindustries.com

 

[codym]

I true velocity out to 600 yards beyond that I true BC

 

[wind gypsy]

something to consider- having solid chrono numbers from a recent range trip and using that velocity while gathering dope is different than knowing what the velocity was on the shots you’re using to true or gather dope. This is where the Doppler chronos really shine because you can know the velocity the shot you’re trueing with.

 

[Shortschaf]

I always wondered what you do if you get solid chrono numbers but when you go to true, you are off

I would look really hard at my atmospheric inputs before changing any of the highly tested bullet BC's (eldm, eldx, berger hybrids, classic hunters, EOL's, etc) by 2%

I have not had to change any of the 6.5 130, 140, or 156 berger BC's at all for 1000+ yards

My opinion is most are hasty to change that when it isnt the root cause

 

[eric1115]

Check scope tracking too before adjusting BC. Entirely possible to have a small error percentage wise that shows up at distance.

 

[huntnful]

I would look really hard at my atmospheric inputs before changing any of the highly tested bullet BC's (eldm, eldx, berger hybrids, classic hunters, EOL's, etc) by 2%

I have not had to change any of the 6.5 130, 140, or 156 berger BC's at all for 1000+ yards

My opinion is most are hasty to change that when it isnt the root cause

Absolutely true.

If you’re off 6” at 6-700 yards, it is likely not your data, if gathered and input correctly. That takes massive adjustments to correct.

I track velocity the whole time and true the BC at 1000-1200 yards. I don’t true velocity any more.

The BC’s are normally extremely close though. So if you don’t have a chrono, absolutely just true the velocity.

I did the calculations on whether or not it made a difference in ballistic data. At 1000 yards, whether you true BC or Velocity for a 6” difference in impact made almost no difference as far as the corrected drop data was concerned. So it really does not matter that much under 1000 yards with a decent cartridge and bullet.

 

[bojangles808]

something to consider- having solid chrono numbers from a recent range trip and using that velocity while gathering dope is different than knowing what the velocity was on the shots you’re using to true or gather dope. This is where the Doppler chronos really shine because you can know the velocity the shot you’re trueing with.

yea I do have a garmin but then there's the SD too. Higher SDs probably mean its more the MV than the bullet? Probably limits me with factory ammo, but where does it start be a problem in the 20s? 30s? I thought it was looking at my last couple range session, but I'm usually in the 20s with factory 108s and teens with 140s

 

[MOwhitetail]

Absolutely true.

If you’re off 6” at 6-700 yards, it is likely not your data, if gathered and input correctly. That takes massive adjustments to correct.

I track velocity the whole time and true the BC at 1000-1200 yards. I don’t true velocity any more.

The BC’s are normally extremely close though. So if you don’t have a chrono, absolutely just true the velocity.

I did the calculations on whether or not it made a difference in ballistic data. At 1000 yards, whether you true BC or Velocity for a 6” difference in impact made almost no difference as far as the corrected drop data was concerned. So it really does not matter that much under 1000 yards with a decent cartridge and bullet.

How do you track velocity at that distance?

 

[huntnful]

How do you track velocity at that distance?

Tracking it as in monitoring it when I’m truing at distance. Still just using the MV

 

[Shortschaf]

Monitor ES, not SD. Plug in lowest velocities and highest velocities you expect/chrono, and check the difference in drop at some distance. If its too much vertical spread for your application, ES is too high

 

[Lawnboi]

Really depends on the range, conditions and knowledge.

I’d bet most people are trueing to conditions, or issues with their rifle system.