Truing MV vs BC

[Edinburgh Rifles]

Ballistic Coefficient is not a constant

It is a function of Velocity,
You cant change one without changing the other
BC changes all the way out as the bullet travels and slows down.

not many bullet manufacturers publish BC within specific velocity ranges, Sierra do
Most just publish BC within a specific test environment of 100m using the Muzzle (or as close to it as possible) and the terminal

It doesn't take into consideration altitude, pressure and temperature on the day

High numbers are good for marketing
in real terms they are not always accurate and Ballistic calculators use the base figure to attempt calculations at a range of initial and terminal velocities

you can manipulate either or both of them to tie into known, field trajectory data

 

[s8mdevo]

Ballistic Coefficient is not a constant

It is a function of Velocity,
You cant change one without changing the other
BC changes all the way out as the bullet travels and slows down.

not many bullet manufacturers publish BC within specific velocity ranges, Sierra do
Most just publish BC within a specific test environment of 100m using the Muzzle (or as close to it as possible) and the terminal

It doesn't take into consideration altitude, pressure and temperature on the day

High numbers are good for marketing
in real terms they are not always accurate and Ballistic calculators use the base figure to attempt calculations at a range of initial and terminal velocities

you can manipulate either or both of them to tie into known, field trajectory data

This makes sense, play with both until field data matches the calculator and be done with it. It doesn't really matter what the velocity or bc is in the calculator so long as it matches the equipment.

 

[User00033]

This makes sense, play with both until field data matches the calculator and be done with it. It doesn't really matter what the velocity or bc is in the calculator so long as it matches the equipment.

Exactly. The MV validation in Strelock+ works perfectly for me, no need to fiddle with BC, this for shots out to a maximum of 700yds. That said, we are planning another 600-1200m test soon and the lads are being encouraged to use the Hornady 4DOF calculator and have a think about how BC changes downrange. This will challenge most of us as Strelock+ can't deal with diminishing BC in line with velocity. (Unless is in the code and I just don't know about it).

Its interesting how the advent of these new high BC bullets has gotten us investigating ballistics far more than ever before. Its definitely a function of the bullets' improved terminal performance, and better ballistics than traditional soft points past normal hunting ranges... its got our attention.

 

[MarkT]

Ed is as far as I understand , correct in that BC is not a constant and the BC changes along its flight path .Also the G1 coefficient was developed on a bullet model with a 2 diameter radius and a flat base not really appropriate for VLD bullets . The G7 coefficient is more appropriate as the bullet model is based on a 10 bullet diameter radius secant with a 7.5 degree boat tail .Ditch the G1 and use Strelok Pro, you can trim the BC in the settings and make use of the internal barometer .Also if your rangefinder gives an equivalent horizontal distance use this.
Sorry got tired of being humble and felt the need for a rant .
Straight lead.

 

[User00033]

This article helped me get my head around things... a good introduction at least. Still so much to learn...

https://www.hornady.com/team-hornady/ballistic-calculators/ballistic-resources/external-ballistics

And this one helps with the selection of BC according to range.

https://www.hornady.com/support/ballistic-coefficient

MarkT - that wasn't a rant!!!

 

[MarkT]

dodgyknees- For me that was a rant .
I'm not an expert in ballistics but have a reasonable understanding. I've spent a lot of time trying to get the best out of Strelok pro and I think it was Chester P who told me they take a little driving.
At a 1000 yards you will need to use the coriolis and azimuth setting, a true west shot would be a possible 3 inch low and east 3 inch high at that distance .
As Laurie pointed out there's so many variables .The greater the distances the better the info required by the app.
I found if you use the manufacturer BC , find the point at which accuracy goes off then look at the calculated Velocity for the last known accuracy point and trim the BC in the settings accordingly. I had to do this twice to get beyond 600 yards accurately .
Strelok Pro is a huge step forward on Strelok + and can be adjusted for more variables including altitude and barometric pressure. A lot of these things can need adjusting on the day.
Wind drift is far harder to deal with , as it can change along the flight path.
Think that's everything. Driving lesson over.
Straight lead to you all
Mark

 

[User00033]

I appreciate the tips very much. Like I said, so much to learn. I've said it before on here, when things are set up properly and theres been some practice beforehand, shooting at 600 yards is relatively straightforward on a calm day. I find it infinitely easier with a low recoiling rifle. But at 1,000yds, I'm pretty hopeless. Strelock+ is about to get upgraded. And the books are out, on the dining room table...

 

[MarkT]

I appreciate the tips very much. Like I said, so much to learn. I've said it before on here, when things are set up properly and theres been some practice beforehand, shooting at 600 yards is relatively straightforward on a calm day. I find it infinitely easier with a low recoiling rifle. But at 1,000yds, I'm pretty hopeless. Strelock+ is about to get upgraded. And the books are out, on the dining room table...

Hope I didn't come across as a smart ass . I would say that to get it bang on requires a little time, 1 click out at 400 yards on a rabbits head could be a clean miss but a clean hit on a 4" gong , just an example ,but you see my point.It's what is acceptable to the user .
Stick with it and enjoy.

 

[swarovski]

Sendaro you didn't say what range you were zeroed in at.i just entered in data for 300wm for the bullet you used with Litz's BC of .570 and the zero temps etc to match my 7mm Saum and your load is flatter than i thought but still not as flat as the Saum on 180gr berger hybrids. Mine is 100yds zero

 

[Laurie]

With known distance (KD) target shooting, life is relatively easy. Getting come-ups for one distance (eg 600) makes it much easier to be 'on', first time out at 800 or 1,000. The important thing is to have a good zero for a load and to keep sight-setting records. This not only gives a 'typical' come-up from say 100 to 1,000 at a particular range, but gives an indication of how different conditions affect the required settings. For instance there can be a 2-MOA elevation adjustment difference at 1,000 yards for a 6.5 or 7mm at Diggle between the prevailing 5 o'clock wind and strong headwind conditions, even more for a 308.

The huge advances in equipment, apps, aids of various sorts if used professionally come into their own though for unknown distance extreme range varminting, military sniping and suchlike or in the KD competition arena ELR (extended long-range) shooting. If not familiar with it, have a look at the 'King of Two Miles', an annual sudden death type comp where shooters have three shots each at plate targets at 1,543, 1,722, 1,888, 1,953, 2,667, and 3,368 yards ranges.

http://bulletin.accurateshooter.com/2017/07/king-of-2-miles-elr-match-derek-rodgers-takes-the-crown/

'Sudden Death'? No sighters and competitors get three shots only at each distance up to 1,953 yards (5 shots at each range for those further out). A failure to connect with at least one sees the competitor fall out for the next and subsequent stages, although all points accumulated up to that point remain valid.

Despite the use of exotic powerful cartridges, machined ballistic missile shape bullets and fancy wind and environmental measurement equipment, remianing on target at over 3,000 yards requires very sophisticated equipment, powerful (and individually tailored) ballistic programs with custom adjustments for actual recorded bullet behaviours, and judgement on how conditions on the day a couple of thousand yards from the muzzle are going to affect bullets. Same for people shooting gallon milk jugs at 1 mile with factory rifles and suchlike.

This has become such a science or area of skills / knowledge in itself that Bryan Litz's company Applied Ballistics LLC is now running several two or three days per annum courses in setting up and customising the programs / apps (as well as supplying and updating them) and in actual LR field use.

 

[s8mdevo]

Sendaro you didn't say what range you were zeroed in at.i just entered in data for 300wm for the bullet you used with Litz's BC of .570 and the zero temps etc to match my 7mm Saum and your load is flatter than i thought but still not as flat as the Saum on 180gr berger hybrids. Mine is 100yds zero

I'm zeroed at 200yd

 

[MTLEADFARMER]

http://www.appliedballisticsllc.com/Articles/BallisticCalibration.pdf

 

[s8mdevo]

http://www.appliedballisticsllc.com/Articles/BallisticCalibration.pdf

Thank you, exactly what I was after.