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Inclined Fire - a technical discussion.


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47 minutes ago, Popsbengo said:

"....So the flight time is still your theoretical 2secs, the fact is that, the bullet is only being effected by gravity for 0.866% of the flight, which due to the inclined or declined angle gives a ballistic advantage, the direct result of which is the need to allow for less drop for the given distance. "

How's that? surely the bullet is under gravitational effects immediately it leaves the barrel 

AB e is giving me a flight time of 1.16 secs 

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59 minutes ago, Popsbengo said:

"....So the flight time is still your theoretical 2secs, the fact is that, the bullet is only being effected by gravity for 0.866% of the flight, which due to the inclined or declined angle gives a ballistic advantage, the direct result of which is the need to allow for less drop for the given distance. "

How's that? surely the bullet is under gravitational effects immediately it leaves the barrel 

Beggin' pardon for pedantry, pops, but gravity is affecting the bullet all the time. Even when it's in the barrel too. 

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5 hours ago, Ronin said:

 You need to get your solution system into an app BD - serious suggestion, the cards worked brilliantly, but an app would be easier on my old and rather tired eyes 

👍🏻

Plus 1; the cards a simple and intuitive. 

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7 minutes ago, meles meles said:

Beggin' pardon for pedantry, pops, but gravity is affecting the bullet all the time. Even when it's in the barrel too. 

well yes, but you know what I mean Badger !  Surely the bullet is falling towards the centre of the earth as it leaves the muzzle so there's a compound vector

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Gravity is a constant 9.8mtrs per second Squared it doesn’t stop or go away 

Unless your being waterboarded on a CIA interrogations plane ,,,,

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3 hours ago, Cheetor said:

 

The rest of your statement is just clouding the issue, the bullet still travels the 1000 mtrs to the target, correct. So the flight time is still your theoretical 2secs, the fact is that, the bullet is only being effected by gravity for 0.866% of the flight, which due to the inclined or declined angle gives a ballistic advantage, the direct result of which is the need to allow for less drop for the given distance. 

It doesn't just appear to drop less, it actually does drop less.

That's simply incorrect 😊

To understand what's happening, you'll need to think of gravity as an acceleration (which it is!), and the vectors at play.

...if it's in the air for 2 secs, it's being accelerated by gravity for 2 secs. [Noting meles's point, which is correct but doesn't help in explaining the concepts!😂]   The horizontal distance it crosses is irrelevant.   (Think about it,  by that reasoning, something let go from a hand wouldn't drop, because it covers 0 horizontal distance!)

The pencil illustration isn't a clouding, it's an illustration of the vectors at play.

I'm sure the intent was to enlighten, mine too, but with the correct info 😊

If that's not to your taste, read up on it - I see Applied Ballistics touted as the best read; certainly  everything I've seen of Bryan Litz's has been spot on, so worth a look, I would think 😊

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1 hour ago, Gandy said:

Plus 1; the cards a simple and intuitive. 

I haven't done those for years - only did those when the ASAT bloke asked me  if I could create a mk2 card for him that had multiple winds and (precessional) drift on them... and became fascinated by the solution - as did a couple of others on here who went on to come up with even cleverer things.  ASAT bloke was a marmite chap, but for all that, he knew his external ballistics.  Funnily enough, discussing theory of inclined fire is how I sussed that he actually understood what he was talking about.  (Cheeky bugger said the same thing to me 😂)   Inclined Fire theory is a bit of an 'understanding'  litmus test .

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7 minutes ago, terryh said:

‘Precessional drift’ 😳, you’ll be throwing in Magnus effect next 🤔😂😂 ( which I’d actually be interested in for BPCR’s)

Hmmm Magnus effect  Although pretty insignificant on a bullets flight path it’s still a very interesting phenomenon.  🤔 

stop it FFS .

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1 hour ago, One on top of two said:

Hmmm Magnus effect  Although pretty insignificant on a bullets flight path it’s still a very interesting phenomenon.  🤔 

stop it FFS .

bend it like Beckham 😁

 

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2 hours ago, One on top of two said:

Hmmm Magnus effect  Although pretty insignificant on a bullets flight path it’s still a very interesting phenomenon.  🤔 

stop it FFS .

It worked for Barnes Wallis 🙂 (though not exactly on the flight path)

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Gents,

apologies for going off OP but.....

Only ever experienced this in the BPCR's I referred to, big slow moving bullets. Wind in the morning blowing L-R = an set of elevations for each distance. In the afternoon blowing R-L = change in elevation with all other factors, temp etc. pretty much the same.

Don't think it's relevant for fast small 'wind cheater' bullets which are the context of this thread.

T

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28 minutes ago, terryh said:

Gents,

apologies for going off OP but.....

Only ever experienced this in the BPCR's I referred to, big slow moving bullets. Wind in the morning blowing L-R = an set of elevations for each distance. In the afternoon blowing R-L = change in elevation with all other factors, temp etc. pretty much the same.

Don't think it's relevant for fast small 'wind cheater' bullets which are the context of this thread.

T

It’s a cracking subject terry. I think your right about the smaller fast stuff but definitely has an Impact on big slow  jumbo jet calibres like the 45/70 ect ect  especially in the smooth bore black powder patched stuff 👍

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4 hours ago, Popsbengo said:

well yes, but you know what I mean Badger !  Surely the bullet is falling towards the centre of the earth as it leaves the muzzle so there's a compound vector

One could put up a good argument that the bullet isn't falling, rather the earth is rising up towards it. Newtonian equivalency and all that...

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  • 2 weeks later...
On 24 April 2020 at 10:00 AM, tackb said:

seeing how well you did last year mate and how badly some of the internet shooters have done i'm inclined towards your method , it's easy to make hits when typing at a keyboard but in reality under pressure during the stage most plans turn to ratsh1t and it's the shooters that can react organically under pressure doing it for real that score well. 

and well done young jedi for some brilliant performances last year ! 

THANKS TERRY Wish this virus would hurry the hell up and let me get back to shooting now. 

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In the video clip the Main stage appears to be being shot on the raised platform - there are two distinct shouts from scorers shouting “ impact “ - I guess from someone shooting another stage nearby 

Another shooter seems to get behind a rifle on the lower right of the screen - is that a third stage shooting across (underneath) the main chap on the kneeling / standing positions ?

 

 

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There were at least 4 stages being shot in that area concurrently, usually two on the platform and one just off either side. Just looking at the video clip again there were three shooter on the platform, one prone on far left, one in a box in the middle and the guy changing position on the right. All shooting at different targets at different ranges spread around the valley.

 

 

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Cheers for that John

 

As others have said - looking forward to being able to start plate comps again once restrictions lifted 

 

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Magnus effect.....lets throw in "dynamic jump" too and how that's affected by global positioning just to muddy the waters a bit more 😂

I was once "beasted" on a shooting course for daring to suggest your point of aim should lower with a downhill or uphill shot.  I didn't know the maths then but had done enough shooting to realise it was a truth.  Trouble is neither did the Colour who thought I was being a smartarse so made an example of me!.....and looking back on it quite rightly as in battle conditions it was another complication a section didn't need.

Back to the present and if in doubt about my ballistics theory, Litz's Applied Ballistics for Long Range Shooting is on my shelf and comes out quite often.  For those who can patiently follow the maths (and there's a lot of it) it makes perfect sense. As BD has pointed out, you simply treat it as a vector and work out the effects of gravity and the effects of the other components such as drag, to come up with the answer.  In simple terms, because I'm a simple chap, the explanation is that once the line of sight to the target is anything other than horizontal,  gravity remains a constant (downwards part of the vector) and acts to pull the bullet away from the line of sight,  gravity both helps slow the bullet (acceleration acting against the bullet's horizontal  inertia) and since the horizontal vector is the horizontal to the target from the firing point, gravity acts over a shorter horizontal distance (ie the 9.81m/s acts vertically downwards, not at an angle perpendicular to the arc of flight when inclined or declined) hence the projectile doesn't fall as far under the line of sight as if the target was horizontal.  It took a while for me to get my head around that but Litz explains it well (see P47 of Applied Ballistics).

The "Shooters' Rule" is an approximation of the affets of up or downhill shooting and more advanced ballistics apps ask for this angle and do the simple calculation based on the "Shooters' Rule"

This rule is simply: Multiply range to target by the Cosine of the Look angle.  This gives you the approximate horizontal range to the target which you then use in your bullet drop calcs.  However, this approximation doesn't allow for the other constant that is NOT affected by incline, which is drag, so technically you should also apply apply the drag of the actual trajectory distance and the gravity part of the Cosine of the Look angle and this gives the more accurate drop.  You could go on refining it further but this is as far as most tend to go.   As long as you understand the principles and know how to use your app, or can approximate angles and use even a phone to work out the cosine you have a quick reference.  For hunting inside 400 yds I would suggest KISS principle applies!  Litz maintains that  the way to apply the drag coefficient (and this is genius) is simply to modify the G7 BC to be less than it actually is so that there is a proportionality between look angle and BC correction factor, and this is the modified factor used together with the horizontal distance which gives the best approximation of actual drop.

He proposes that a scale factor "f" is used to modify BC where:

 

f= 1+1.3 x 10 (to the -5) x h

 

where "h" is the difference in altitude between the shooter and the target.

Fore clarity, I'll use his worked example below for a 155gr .308 bullet with an MV of 3000fps and a G7 of 0.233:

Look angle is for this example 45 degrees and target is at 1000 yards at a 45 degree look up angle.  Drop below target without correction is calculated as -219.3".

 

From the Cosine rule h = 2000x Sin(45) = 1414ft  (note Brian has made an error in the book and used the MV instead of the distance!) so the target is 1414ft above the shooter;

If the shot were downhill the target would be at -1414 ft;

Using the correction factor equation, we have:

f= 1 + 1.3 (10 to the -5) x 1414 = 1.018

So for this shot, you would correct the BC by 1.018 so BC (corrected) would become 0.223 x 1.018 = 0.227 and that is what you would use in your calculator for 1000 yds.

Best really to read his fairly short chapter on this if still confused!

 

 

 

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If you're interestd in the Maths of this then try Elements of Exterior Ballistics by George Klimi.

Its very maths heavy though, lots of inverse trig funcions and even an entire chaper on the differential equations of exterior Ballistics.

 

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