Thread: "Trueing" BC/Velocity

Originally Posted by Moutere

Advice: Tordon at label rates would tidy that gorse up nicely, metsulfuron if you were on a budget and happy wait longer.

Nice shooting.

Met will tidy a lot of things up

Originally Posted by Stocky

Watch/listen to hornady 4dof app pretty much explains why trueing is a shot yarn if you ahbe a reliable chrono and will at something lead to significant erro at some range.

See it's a question starter not an actual question stand by those podcasts very good

Further to this, all of the podcasts that are about external ballistics and drag are well worth a watch (or listen). Though I think that starting with 'Your groups are too small' parts 1 and 2 gives the useful grounding on statistical significance. Once you understand the importance of statistical significance the rest of the discussion (including critiques of load methodologies) makes a lot more sense.

If you are running a pretty std velocity for the bullet ie a 140 6.5 where you are in that 2750-2900 fps then the BC in your app will be pretty right and just adjust the velocity to correct your drop. If you happen to be running it in a caliber that is going quite a bit faster then you might increase bc slightly and if going a lot slower ie in a Grendel or very short barrel then you would drop the BC. Some bullet manufacturers like Sierra have banded (different velocity thresholds) BC listed. Using a good app with good actual bc data like Applied ballistics BC are more accurate. Running some apps where they use the manufacturers no.s like nosler or Barnes where they maybe slightly over stated you may need to adjust. For std hunting we usually shoot 800m and use that drop for adjusting velocity. Some apps allow you to put in actual drop and will work out velocity for you. Snipers hide has a new app called gravity balistics that will do your dope without using velocity or BC and uses a multiplier but you need targets every 100m. You can true your drop at 600m. Works fine, the closer to your transonic about 1400 fps the better for further accurate drop prediction. Make sure settings are all correct such as scope height above bore and zero range as those 2 factors make a difference. Once getting out to distance atmospheric inputs on day of doing data may make a bit of difference when you shoot again also. Aswell as shooting direction as shooting north south makes a windage error and east west makes a elevation error. Depending on whether your app has a calculation worked in for that. Inside 500m a lot of these factors are minimal. I like to write my drop data in a book when truing a rifle so I can reference if I have trouble with an app or get another one and want the correct inputs.
We do run shooting schools at Sparrowhawknz that teach this, check out the website.

Using g7 bc will give you better longer range data than g1. If you have a modern boat tail bullet use the g7 bc.

Insufficient data to comment.

Multiple 5 shot groups required to improve quality and quality of data set.

Physics is fascinating, but most people can’t be bothered to generate sufficient quality data to formulate quality outputs. Even if they do understand most of the factors involved.

Me, I’d just end up calling it a 1/4 Moa gun and probably sell it

Just get applied ballistics and use a custom curve. BC is not a static number over different velocities

Originally Posted by veitnamcam

If there is any vertical discrepancy I cant attribute to wind then I adjust velocity in app untill it matches results.
My reasoning is as follows.
Bryan Litz bcs are probably pretty accurate.
My shooting chrony is probably within 100fps on a good day.

I agree. Tune mv to match real world. Should only be a few tenths out, otherwise something more serious is wrong e.g. zero or environmentals
True BC if I have access to significant sub-sonic range (e.g. 1k+)

Are you bloody kidding Gimp!!

It's a pretty easy process. What you do is write down how many clicks it was to 600m on your wrist mounted diary, or failing that inside your scope caps next to you punisher sticker.

Then when you are next out hunting, find a deer check your wrist diary, apply a Little more face paint and dial up your nightforce then walk backwards until you are 600 yards away and send it.

Easy

Originally Posted by Cowboy06

If you are running a pretty std velocity for the bullet ie a 140 6.5 where you are in that 2750-2900 fps then the BC in your app will be pretty right and just adjust the velocity to correct your drop. If you happen to be running it in a caliber that is going quite a bit faster then you might increase bc slightly and if going a lot slower ie in a Grendel or very short barrel then you would drop the BC. Some bullet manufacturers like Sierra have banded (different velocity thresholds) BC listed. Using a good app with good actual bc data like Applied ballistics BC are more accurate. Running some apps where they use the manufacturers no.s like nosler or Barnes where they maybe slightly over stated you may need to adjust. For std hunting we usually shoot 800m and use that drop for adjusting velocity. Some apps allow you to put in actual drop and will work out velocity for you. Snipers hide has a new app called gravity balistics that will do your dope without using velocity or BC and uses a multiplier but you need targets every 100m. You can true your drop at 600m. Works fine, the closer to your transonic about 1400 fps the better for further accurate drop prediction. Make sure settings are all correct such as scope height above bore and zero range as those 2 factors make a difference. Once getting out to distance atmospheric inputs on day of doing data may make a bit of difference when you shoot again also. Aswell as shooting direction as shooting north south makes a windage error and east west makes a elevation error. Depending on whether your app has a calculation worked in for that. Inside 500m a lot of these factors are minimal. I like to write my drop data in a book when truing a rifle so I can reference if I have trouble with an app or get another one and want the correct inputs.
We do run shooting schools at Sparrowhawknz that teach this, check out the website.

What he said.
Bullshit in bullshit out.
Perfect zero is a very good start.
Watch some litz or todd and Colby hodnett videos on truing.

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