Tipping Bullets & Custom Drag Curve Modeling

[parshal]

I haven't been able to find an answer to this directly but I'm sure it's been asked and answered somewhere that I can't find.

I've got a Kestrel 5700 Elite. I'm shooting both a 22 Creedmoor. with 82 grain Bergers at 3500 fps as measured by my Magnetospeed. I've measured velocity at varying temperatures so I can plug in the temps in the muzzle velocity table. I'm using the custom drag curve for the bullet in the Kestrel. The range I normally use only goes out to 600 yards although I infrequently shoot farther but have no regular access to a range that far.

If I trim the meplats and point the bullets I know I'm changing the BC. What is the best process for figuring out the new BC? Would I calibrate the velocity even though I've got that information from the Magnetospeed? I can't exactly calibrate the DSF since I don't have regular access to a range to shoot far enough to get into the transonic and subsonic range. I'm sure there's a pretty straightforward answer out there somewhere.

I have both Strelok Pro and Kestrel Link on my iPhone but have been using Kestrel more frequently.

 

[BergerFan222]

There are some resources out there describing how to measure BCs with the new LabRadar.

Google something like

Measuring free flight drag with doppler radar

One link is:

https://www.shootingsoftware.com/doppler.htm

 

[parshal]

Thanks Berger. I had a LabRadar and talking to the guy that distributes them he said they weren't powerful enough to get a true BC reading. However, the article you linked certainly would state otherwise. I used the LR for a few months and loved it. However, I couldn't get it to consistently read at my 600 yard covered range. We worked on it for a while and replaced it twice and I still couldn't get it to work right. We never could figure out what it was.

What I'm curious about is whether I can modify the custom drag curve to reflect the changed BC from pointing bullets. Or, am I better off creating a new one by measuring drop? I'm not completely versed in the Kestrel AB. I know how to do it in Strelok Pro.

From more reading, it looks like I need to calibrate the muzzle velocity to make adjustments within supersonic ranges.

 

[Mikecr]

When it comes to 1st shot accuracy (not just getting on paper), I don't think a single muzzle velocity adjustment will work so well across a gamut of ranges -for a drag curve discrepancy.

The issue we've had with G1 BCs is that the curve wasn't a match for higher BC bullets in use. Basically,, your situation.
With this, our solutions would be right at this or that range, but not both. We could adjust MV to make a particular range solution right, but this departs from an adjustment made at another range, undoing it.. So to make G1 solutions right across many ranges took varying MV adjustments at many ranges. We're talking manual operations, a lot of time & testing, to create a better field click card.

Going to a better match curve for many bullets (G7), reduced the amplitude of discrepancies across supersonic ranges (at least). For many, this in itself made everything good enough.
This is an entire curve change, with different math conveniently selected in software that allows it. YOUR modified bullet drag will not fit G7, or G5, or matching that of any standard (amplitude wise). I don't know if your AB software allows construction of a custom curve.

You could shift application of a standard curve with an air density bias.
With a Kestrel For instance you could shift pressure from 29.92 @ SL to 28.85 (a miscalibration).
With that your solutions are still following a curve at the correct velocity points(range), while biased for less effective drag at each point.

It's something to consider. You will never know how your modified bullet actually changes the shape of it's drag curve. But if it doesn't change the shape(just amplitude), and a selected curve suits, you could lock in adjusted solutions to that selected curve.
This might work right across your various ranges of shooting.

 

[BergerFan222]

Thanks Berger. I had a LabRadar and talking to the guy that distributes them he said they weren't powerful enough to get a true BC reading. However, the article you linked certainly would state otherwise. I used the LR for a few months and loved it. However, I couldn't get it to consistently read at my 600 yard covered range. We worked on it for a while and replaced it twice and I still couldn't get it to work right. We never could figure out what it was.

Yeah, like a lot of newer products, some people are experiencing the growing pains.

We're having success measuring G7 BCs which don't seem to change too much with velocity and are also very close to what the manufacturers are reporting in the case of unmodified bullets. Our approach to generating G7 values for different velocities is to use reduced powder charges (since the LabRadar range is limited to 100 yards). It's not too hard to map out 4-5 G7 BCs spanning the while supersonic range. We've done a few into the subsonic range also.