Magnum caliber truing distances

[912173]

Anybody have recommendations for distances to true kestrel ballistics with a 300 Norma? This is a 230gr Berger hybrid target going 2960s according to my magnetospeed. Kestrel said 7.6 mils to 1170yds and I ended with 7.8 which trues to 2940 fps if I adjust velocity. Is this a reasonable velocity distance for a high performance caliber? I'm trying to get the curve sorted out as efficienty as possible and I'm betting the yardages I used for my .308 aren't going to work well.

 

[_Windrider_]

You could do it the same as any other truing. @lowlight generally recommends 600 for MV and 800 for BC and those are good numbers for the distances most have access too, especially for 30 cal bullets. Ive gotten away with MV truing as far out as 1k and i try to do a BC true right around transonic or as close as possible.

 

[912173]

Thanks for the reply! The 1170 target was already up so that's why I used it. Next time I go out I'll probably shoot a 600 or 800 to check velocity and then go out to transonic for bc. Once that's done I'll probably play with drop scale factor to get out to my elevation limit. I was going to ask Frank during his class in August but I didn't get a chance.

 

[ma smith]

There is a Berger Bullets podcast series called "no BS BC" I'd start there, from the Horse's mouth. Brian Litz is on the podcast, so everything else you read on the internet is going to risk having some distortions IMHO.

Variation in BC with Velocity

Any bullet can have both a G1 and a G7 BC, it’s just a matter which one is more representative for all speeds. G7 BC is typically more reliable.

bergerbullets.com

Custom Drag Models for Extreme Long Range

Figure 1. The G7 model is a much better fit to this bullet, but there is still some minor mis-match. Most shooters are familiar with Ballistic Coefficients (BC’s) as a performance metric for bullets. If you’ve been reading other articles in this series, you know that a

bergerbullets.com

IIRc the correct ditances are a function of mach numbers which will vary by caliber/load etc.

Check out the pic related and this will make more sense.

A legit doppler/etc G7 BC may not need to be trued very much until it it gets to mach 1.5

 

[ma smith]

Fwiw, heres another interesting image showing a "trued" curve (CDM)

 

[912173]

I did listen to those episodes, I'll probably go back and listen again because it was a while back. I thought they approved of the small tweaks to line the computer model up to actual dope.

 

[_Windrider_]

I did listen to those episodes, I'll probably go back and listen again because it was a while back. I thought they approved of the small tweaks to line the computer model up to actual dope.

They do but what they push is the CDM’s. Which are better but also are not free.

 

[Long Range 338]

It’s been my experience that the CDMs work very well whereas truing can take a fair more adjustment. As mentioned above you would true velocity, then bc, and lastly dsf.

 

[Steel head]

I’ve had hit or miss experience with CDM’s

I always just use muzzle speed and BC(with Berger bullets) then use the kestrel truing function and Then DSF if needed for subsonic.
Rarely is it more that 20fps change and if it’s more a bit of a BC tweak might be in order.

If it’s really wonky I always question unseen conditions, take notes and try again later.

 

[ma smith]

Cal DSF should only be used in the trans/subsonic regions. And you should enter them from closest to longest correction. For instance if you make a Cal DSF at 1500 yards, and then make another at 1300 yards, the 1500 yard one will be disregarded. You should enter one at 1300 and then 1500 (if still necessary) in that order in this example (again as long as this is at least transonic region)

In aeronautics, transonic refers to ...speed of sound in the range of Mach 0.8 to 1.2.

This suggest you would be looking for mach 1.2 to 1.1 which is what I recal Litz saying. For 300NM I think you are looking at ±1400 type numbers if Mach 1 is ±1600yd. But I hesitate to say anything other than run your actual numnbers and then follow what AB/Litz actually says, because I don't want to misquote it. All assuming you have a kestrel with DSF, of course.

 

[Clearlight]

After loading a new lot number of H1000 in my 300 NM with 230 Hybrid, I trued @ 1360
and used the appropriate drag curve supplied in the Garmin 701. Good solutions to 2200
so far, seems the new batch of powder is slightly spicier than the old one, had to add 25
fps and everything lined up perfectly. I vaguely recall Bryan and Doc B recommending
about 3/4 of your supersonic range as a reasonable point to true your solution, happy
to be corrected if I’m off about that.

EDIT: that load is ss to about 1700, at that firing point.

 

[_Windrider_]

After loading a new lot number of H1000 in my 300 NM with 230 Hybrid, I trued @ 1360
and used the appropriate drag curve supplied in the Garmin 701. Good solutions to 2200
so far, seems the new batch of powder is slightly spicier than the old one, had to add 25
fps and everything lined up perfectly. I vaguely recall Bryan and Doc B recommending
about 3/4 of your supersonic range as a reasonable point to true your solution, happy
to be corrected if I’m off about that.

EDIT: that load is ss to about 1700, at that firing point.

You ever get that stiller fixed?

 

[Clearlight]

^^ Yes ! Stiller were great and send me a new cocking piece, and a spare. Thanks Stiller

 

[Shoots 700's]

Not sure if this works for everyone, but I have been truing on our 10" 1000 yard plate.

 

[912173]

So almost a year later now I finally stretched out my 300 Norma to check my Kestrel curve. I used my big 24"x24" plate and used the curve I trued from the 1170yd data I mentioned at the start of this thread. I drove back from the target to 1150 where I got center hits with 7.6mils just as the kestrel predicted. At 1466yds, the kestrel said 11.21 and I settled on 11.0mils. Due to terrain, the next distance that I could get line of sight was 2221 yards. The Kestrel said 23.75 mils and I got a third round hit using 23.5. If I were to change mv to line up the data, it goes from 2940 to 2952 but I'm not changing anything unless I get more data. Being within .2 mils past 2000 yards is crazy considering all I did was zero the gun and line it up at 1170 last year. I guess it probably helps that the same guy was involved with designing the bullet and the software. This was using an early circa 2012 non-bluetooth applied ballistics kestrel.

 

[Lite]

So almost a year later now I finally stretched out my 300 Norma to check my Kestrel curve. I used my big 24"x24" plate and used the curve I trued from the 1170yd data I mentioned at the start of this thread. I drove back from the target to 1150 where I got center hits with 7.6mils just as the kestrel predicted. At 1466yds, the kestrel said 11.21 and I settled on 11.0mils. Due to terrain, the next distance that I could get line of sight was 2221 yards. The Kestrel said 23.75 mils and I got a third round hit using 23.5. If I were to change mv to line up the data, it goes from 2940 to 2952 but I'm not changing anything unless I get more data. Being within .2 mils past 2000 yards is crazy considering all I did was zero the gun and line it up at 1170 last year. I guess it probably helps that the same guy was involved with designing the bullet and the software. This was using an early circa 2012 non-bluetooth applied ballistics kestrel.

I would not change a thing either what that data! Your post made me smile because like you, my 300 Norma Magnum has been very consistent out to 1 mile for me, and I trued the Kestrel at 1,200 meters only because that was the longest truning bar I had available to me. I have not done the math to say if that was the best range for truing (actually the Kestrel will tell you the best range), but we have trued several rifles at 1,200 meters and then moved to the 1 mile and had first round hits, or at least elevation that was spot on. Of course, we were using appropriate cartridges and bullets for 1 mile shooting. Just proves to me that elevation is science, wind is art.