(please) Help me understand these ballistics

[Doing my part]

I just picked up some sako plinking ammo and the claimed ballistics raised an eyebrow. Can someone check I'm not taking crazy pills please?

Yard drop(in)
0. - 1.8
50. 0.1
100. 0.7
150. 0
200. - 2.1
250. - 5.7
300. - 10.9

This looks to me like a 150yd zero (why?) with the bullet climbing to a max height at 100yd and passing the zero after starting to descend.

It feels like quite an abrupt change from climbing 0.6 of an inch between 50 and 100 yards, to dropping 0.7 inch between 100 and 150, then 2.1 inches between 150 and 200.

I suppose looking at the numbers again it's roughly a symmetrical parabola either side of 100yds if you account for a little bit of drag.

I think I get it but something about it feels wrong. Am I in the ballpark? I'm trying to prepare some dope for how I expect it to behave, to compare with actual performance.

 

[Dthomas3523]

Who knows what zero range they used or why. Though it doesn’t matter

You’re also going about dope in a not so great way.

Use your mils or moa needed from your 100yd zero to your target distance as determined by your software and then record actual data.

Or use weaponized math described on this site to determine initial data, then record your actual dope.

Don’t think or use inches for elevation.

 

[Doing my part]

Who knows what zero range they used or why. Though it doesn’t matter

You’re also going about dope in a not so great way.

Use your mils or moa needed from your 100yd zero to your target distance as determined by your software and then record actual data.

Or use weaponized math described on this site to determine initial data, then record your actual dope.

Don’t think or use inches for elevation.

Alright, time for a new paradigm, I will do as told but... (here comes the stupid...) my intention was to use the drop to calculate MOA, and use that as a baseline for scope adjustments. Then record the actual adjustment required.

I'm on the weaponised math(s) path too but I'm a science nerd/engineer so I like to try to understand from first principles, or at least give it a good go to try to prove my model before just shutting up and doing as I'm told

 

[Dthomas3523]

Alright, time for a new paradigm, I will do as told but... (here comes the stupid...) my intention was to use the drop to calculate MOA, and use that as a baseline for scope adjustments. Then record the actual adjustment required.

I'm on the weaponised math(s) path too but I'm a science nerd/engineer so I like to try to understand from first principles, or at least give it a good go to try to prove my model before just shutting up and doing as I'm told

Fine. Waste time.

There’s zero need for linear measurements to be used in dope.

 

[Steel head]

Fine. Waste time.

There’s zero need for linear measurements to be used in dope.

This!
It just unnecessarily complicates things.

 

[Doing my part]

This!
It just unnecessarily complicates things.

OK, sold! JFDI, understood

 

[DocRDS]

OK, sold! JFDI, understood

I think you misunderstand, it is MUCH MUCH simpler to think in angular terms rather than linear terms because you have an angular measurement device in your scope.

Also you might to curve fit to find the max bullet height. There is no guarantee it was at one of the designated intervals.

Third, never trust the mfg spec. Actually its not trust--its for their rifle. Your rifle is different, almost guaranteed.

 

[308pirate]

I just picked up some sako plinking ammo and the claimed ballistics raised an eyebrow. Can someone check I'm not taking crazy pills please?

Yard drop(in)
0. - 1.8
50. 0.1
100. 0.7
150. 0
200. - 2.1
250. - 5.7
300. - 10.9

This looks to me like a 150yd zero (why?) with the bullet climbing to a max height at 100yd and passing the zero after starting to descend.

It feels like quite an abrupt change from climbing 0.6 of an inch between 50 and 100 yards, to dropping 0.7 inch between 100 and 150, then 2.1 inches between 150 and 200.

I suppose looking at the numbers again it's roughly a symmetrical parabola either side of 100yds if you account for a little bit of drag.

I think I get it but something about it feels wrong. Am I in the ballpark? I'm trying to prepare some dope for how I expect it to behave, to compare with actual performance.

They used a 150 yard zero. Why? Who knows? It's just an arbitrary choice, mostly depending on application.

There is nowhere enough data in that drop table to assume that the trajectory apogee is at 100 yards. If you want to know that apogree (aka maximum ordinate) you would have to generate a trajectory table with much finer range increments than 50 yards. More like every 5 or 10 yards.

Bullet trajectory is not a symmetrical parabola. Nowhere near close.

Drop increases rapidly past a certain point because bullet deceleration is not linear.

Go here and play: http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

Engineers (like us) usually have very little trouble understanding this subject once given some basic direction

Linear units for trajectory are useful for some very limited applications, but as a beginner I suggest you ignore them for now.

Thinking and visualizing your trajectory in angular units (minutes of arc or milliradians) is significantly much more useful in reality for about 99% of the time.

 

[Doing my part]

I think you misunderstand, it is MUCH MUCH simpler to think in angular terms rather than linear terms because you have an angular measurement device in your scope.

Also you might to curve fit to find the max bullet height. There is no guarantee it was at one of the designated intervals.

Third, never trust the mfg spec. Actually its not trust--its for their rifle. Your rifle is different, almost guaranteed.

Thanks for this, I appreciate it.

I found the right words to explain what I was aiming to do do - using the mfr numbers to figure out my try-dope. It's in part a result of having a new toy, spreadsheets, and being stuck in lockdown.

Just gotta remember to print the weaponised math(s) tables when I'm not in the office because I don't think I can explain that one to the boss.

 

[Doing my part]

They used a 150 yard zero. Why? Who knows? It's just an arbitrary choice, mostly depending on application.

There is nowhere enough data in that drop table to assume that the trajectory apogee is at 100 yards. If you want to know that apogree (aka maximum ordinate) you would have to generate a trajectory table with much finer range increments than 50 yards. More like every 5 or 10 yards.

Bullet trajectory is not a symmetrical parabola. Nowhere near close.

Drop increases rapidly past a certain point because bullet deceleration is not linear.

Go here and play: http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

Engineers (like us) usually have very little trouble understanding this subject once given some basic direction

Linear units for trajectory are useful for some very limited applications, but as a beginner I suggest you ignore them for now.

Thinking and visualizing your trajectory in angular units (minutes of arc or milliradians) is significantly much more useful in reality for about 99% of the time.

And thanks for this as well. I am absolutely going to try to switch my brain to MOA (that's what all my scopes are) and use the weaponised math, but that doesn't fill time well on extended conference calls.

I was quite looking forward to a conversation about numerical models for bullet behaviour, but after DT's response resigned myself to letting it drop. I'm good either way, don't want to ruffle any feathers but quite enjoy learning the reasoning behind why things are things.

 

[hlee]

Filling time on conference calls is what this site is for... Once you start looking through a scope more, dialing corrections in angular units, and making adjustments using the ruler in your optic (that little cross thingy with the dots and/or hashes), linear measurements will evaporate from your lexicon. Much easier to “do” than to sit and “think.”

 

[308pirate]

I was quite looking forward to a conversation about numerical models for bullet behaviour

I don't think anyone would frown on that here. Those who don't want to participate in the conversation with you are free to stay out of it.

I would buy some books on the topic from an internationally-recognized subject matter expert and get some baseline education first: https://bergerbullets.com/bryan-litz-books/

 

[308pirate]

Filling time on conference calls is what this site is for... Once you start looking through a scope more, dialing corrections in angular units, and making adjustments using the ruler in your optic (that little cross thingy with the dots and/or hashes), linear measurements will evaporate from your lexicon. Much easier to “do” than to sit and “think.”

Unfortunately he's from the UK and it seems they're getting royally (no pun intended) fucked by HM government with closures on just about everything including shooting ranges.

 

[Doing my part]

"that little cross thingy with the dots and/or hashes"

I'm British, not female. I understand what a reticle is.

 

[hlee]

No numbers attached, but here is a graphical representation of the "Why?"

Beyond that, you have the effects of air resistance slowing the bullet as soon as it leaves the muzzle. For every inch the bullet travels, air resistance is slowing the bullet.

And, gravity is not a velocity, but an acceleration 9.8m/s/s. For every millisecond the bullet is in flight, it is increasing its velocity towards earth.

The slowing of the bullet due to air resistance combined with the acceleration towards the earth due to gravity make the bullet path non-parabolic.

 

[hlee]

"that little cross thingy with the dots and/or hashes"

I'm British, not female. I understand what a reticle is.

Some people do not realize that when they buy a scope with a graduated reticle, they are buying a scope with an angular ruler built in to the view (Even british men).

 

[Doing my part]

I see. So I put the hashy liney thingy on the target, then pick the green line because I'm shooting long distance, and then I tell my kestrel to talk to my scope about wind speed then pull the trigger nice and fast so the bullet gets out of the gun before recoil can affect it?

First the reticle jab, then this. I understand that gravity is an acceleration, not a velocity. I understand that air resistance slows things down. Like I said, English, not female.

Here's where I'm at - weaponised maths dopes for gravity, so it assumes 9.82 ms^-2,which gives you your round independent drop. It's also worked in angle so it's in a native language that translates directly to scope hashes. All good so far.

Since gravity is an acceleration, it is more sensitive to elapsed time, which in turn makes MV0 and BC important factors because they'll dictate how much time (and by extension cumulative effect of gravity) will have passed by the time you reach your target. That's why you shoot a bit the re-calibrate your MV from measured data.

To say WM is completely divorced from linear distance actually sounds a little disingenuous to me, since I notice we're measuring the range to the target in yards or metres, and not degrees. Pedantic? Yes, but...

I appreciate the help but I think we can skip a couple of pages.

 

[Doing my part]

That's great. Thanks.

 

[hlee]

I see. So I put the hashy liney thingy on the target, then pick the green line because I'm shooting long distance, and then I tell my kestrel to talk to my scope about wind speed then pull the trigger nice and fast so the bullet gets out of the gun before recoil can affect it?

First the reticle jab, then this. I understand that gravity is an acceleration, not a velocity. I understand that air resistance slows things down. Like I said, English, not female.

Here's where I'm at - weaponised maths dopes for gravity, so it assumes 9.82 ms^-2,which gives you your round independent drop. It's also worked in angle so it's in a native language that translates directly to scope hashes. All good so far.

Since gravity is an acceleration, it is more sensitive to elapsed time, which in turn makes MV0 and BC important factors because they'll dictate how much time (and by extension cumulative effect of gravity) will have passed by the time you reach your target. That's why you shoot a bit the re-calibrate your MV from measured data.

To say WM is completely divorced from linear distance actually sounds a little disingenuous to me, since I notice we're measuring the range to the target in yards or metres, and not degrees. Pedantic? Yes, but...

I appreciate the help but I think we can skip a couple of pages.

"Short" and "long" are arbitrary, because I have not added any numbers. When you zero your rifle, you change the angle of the barrel relative to the line of sight, and can pick any of the bore angles between "red" and the limit of travel on your scope. Typically, we actually choose the blue line for our zero, because this gives us corrections in the same direction (up) for all target distances, whether they are closer to, or more distant than our chosen zero. We can then use the reticle or the dials on our scope to make adjustments. Those adjustments are not made in inches or cm, but in angular units (moa or grad).

Really trying not to be harsh, and 80% of communication is lost in written media. You may be able to skip a few pages, but you certainly should start with chapter 1...

 

[Doing my part]

"Short" and "long" are arbitrary, because I have not added any numbers. When you zero your rifle, you change the angle of the barrel relative to the line of sight, and can pick any of the bore angles between "red" and the limit of travel on your scope. Typically, we actually choose the blue line for our zero, because this gives us corrections in the same direction (up) for all target distances, whether they are closer to, or more distant than our chosen zero. We can then use the reticle or the dials on our scope to make adjustments. Those adjustments are not made in inches or cm, but in angular units (moa or grad).

Really trying not to be harsh, and 80% of communication is lost in written media. You may be able to skip a few pages, but you certainly should start with chapter 1...

Yeah I realised I kicked off a little prematurely. Thanks for your help.

 

[Deleted member 113831]

I just picked up some sako plinking ammo and the claimed ballistics raised an eyebrow. Can someone check I'm not taking crazy pills please?

Yard drop(in)
0. - 1.8
50. 0.1
100. 0.7
150. 0
200. - 2.1
250. - 5.7
300. - 10.9

This looks to me like a 150yd zero (why?) with the bullet climbing to a max height at 100yd and passing the zero after starting to descend.

It feels like quite an abrupt change from climbing 0.6 of an inch between 50 and 100 yards, to dropping 0.7 inch between 100 and 150, then 2.1 inches between 150 and 200.

I suppose looking at the numbers again it's roughly a symmetrical parabola either side of 100yds if you account for a little bit of drag.

I think I get it but something about it feels wrong. Am I in the ballpark? I'm trying to prepare some dope for how I expect it to behave, to compare with actual performance.

It appears to me that the ammunition manufacturer was attempting to provide some type of "maximum point blank range" zero information for the uninitiated shooter.

If you are already on board with a 100 yard zero and actual drop using angular measurements, then you can ignore this.

 

[vh20]

It appears to me that the ammunition manufacturer was attempting to provide some type of "maximum point blank range" zero information for the uninitiated shooter.

If you are already on board with a 100 yard zero and actual drop using angular measurements, then you can ignore this.

Yep

 

[smoothy8500]

I'm British, not female. I understand what a reticle is.

Like I said, English, not female.

Ummm, even my daughter understands how to use MOA and Mils...

 

[Doing my part]

Ummm, even my daughter understands how to use MOA and Mils...

Ah well then, I'll have to refine the model. American female>English male>other females