Welcome guest, is this your first visit? Create Account now to join.
  • Login:

Welcome to the NZ Hunting and Shooting Forums.

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed.

DPT Alpine


User Tag List

+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 15 of 19
Like Tree19Likes

Thread: Angle Compensation

  1. #1
    Member sambnz's Avatar
    Join Date
    Aug 2014
    Location
    Christchurch
    Posts
    420

    Angle Compensation

    Hi Everyone,

    Anyone got any good videos or analogies for explaining the whole angle compensation concept - shooting uphill and downhill vs flat.
    I had a couple shots at some tahr last weekend on a pretty steep uphill angle and couldn't for the life of me figure it out.
    I've heard the saying, Shoot high aim low, shoot low aim low.
    I understand that the bullet will hit lower than expected as the actual distance the bullet is travelling is less, but I don't know how to figure out how much to hold over etc.

    Any help is appreciated.

  2. #2
    A Good Keen Girl Dougie's Avatar
    Join Date
    Jun 2012
    Location
    Hawkes Bay
    Posts
    4,573
    Quick explanation.

    Gravity works his best when on a 90degree angle from whatever it's pulling at. So, gravity is at it's most efficient when your bullet is shot horizontally.

    When you add an angle (up or down is irrelevant), gravity isn't pulling as efficiently as it can. So you will be shooting higher, at the same distance, than if you were shooting horizontally.
    Last edited by Dougie; 06-03-2015 at 09:56 AM.
    She loves the free fresh wind in her hair; Life without care. She's broke but it's oke; that's why the lady is a tramp.

    Rule 4: Identify your target beyond all doubt

  3. #3
    A Good Keen Girl Dougie's Avatar
    Join Date
    Jun 2012
    Location
    Hawkes Bay
    Posts
    4,573
    Quote Originally Posted by sambnz View Post
    Hi Everyone,

    Anyone got any good videos or analogies for explaining the whole angle compensation concept - shooting uphill and downhill vs flat.
    I had a couple shots at some tahr last weekend on a pretty steep uphill angle and couldn't for the life of me figure it out.
    I've heard the saying, Shoot high aim low, shoot low aim low.
    I understand that the bullet will hit lower than expected as the actual distance the bullet is travelling is less, but I don't know how to figure out how much to hold over etc.

    Any help is appreciated.
    And it's not much to do with the distance being travelled being less....actually, that's not really it at all as far as I know. Distance is distance.

    The best way I've found to figure it out is by using a ballistic calculator flick me a PM with your bullet details and I can give you a little drop chart if you like. Just a quick jam on mine with the .223 (I'll use my 55gr load as it will have the most expanded results, by that I mean it will highlight things much more obviously as it is easily affected) and this is what I've come up with:

    Distance; Shot angle; Bullet impact relative to line of sight, in MOA; Bullet impact relative to LOS in Inches
    100; 0; 0; 0.01
    200; 0; 1.7; 3.51
    300; 0; 4.4;13.89

    100; 10; 0; 0.04
    200; 10; 1.6; 3.37
    300; 10; 4.3; 13.55

    100; 20; 0.1; 0.13
    200; 20; 1.4; 2.96
    300; 20; 4.0; 12.52

    100; 30 (that's fucking steep); 0.3; 0.28
    200; 30; 1.1; 2.29
    300; 30; 3.4; 10.83

    I hope that makes some sense.

    EDIT: the reason I have gone back and added the impact relative to LOS but in inches, is to demonstrate that at those longer distances, you can not accurately hold over time and time again. I purposefully used my little bullets to show an exaggerated example, but I think the point is clear. What is 12.52inches? How high is that? What does that look like at 300 yards? How do you aim an entire sika hind's body width higher? These are the little problems my .223 faces without a scope that dials. Luckily for me - I have a scope I can dial with!
    Last edited by Dougie; 06-03-2015 at 10:06 AM.
    She loves the free fresh wind in her hair; Life without care. She's broke but it's oke; that's why the lady is a tramp.

    Rule 4: Identify your target beyond all doubt

  4. #4
    Member
    Join Date
    Jul 2013
    Location
    Tasman
    Posts
    936
    Quote Originally Posted by Dougie View Post
    Quick explanation.

    Gravity works his best when on a 90degree angle from whatever it's pulling at. So, gravity is at it's most efficient when your bullet is shot horizontally.

    When you add an angle (up or down is irrelevant), gravity isn't pulling as efficiently as it can. So you will be shooting higher, at the same distance, than if you were shooting horizontally.
    Gravity is a constant regardless of angle, it is just acting over a shorter horizontal distance than the LOS distance in an angled shot.

  5. #5
    A Good Keen Girl Dougie's Avatar
    Join Date
    Jun 2012
    Location
    Hawkes Bay
    Posts
    4,573
    Quote Originally Posted by Moutere View Post
    Gravity is a constant regardless of angle, it is just acting over a shorter horizontal distance than the LOS distance in an angled shot.
    Yeah, what he said ^^^
    She loves the free fresh wind in her hair; Life without care. She's broke but it's oke; that's why the lady is a tramp.

    Rule 4: Identify your target beyond all doubt

  6. #6
    A Good Keen Girl Dougie's Avatar
    Join Date
    Jun 2012
    Location
    Hawkes Bay
    Posts
    4,573
    That must be where he got the distance thing from, distance travelled vs horizontal distance.

    If you point a range finder uphill though, it says 100yards, then your target is 100yards. However it may be only 50yards of true horizontal travel in which gravity can do its thing on your bullet.
    She loves the free fresh wind in her hair; Life without care. She's broke but it's oke; that's why the lady is a tramp.

    Rule 4: Identify your target beyond all doubt

  7. #7
    Member Bryan's Avatar
    Join Date
    Dec 2011
    Location
    Tauranga
    Posts
    756
    The actual (or true ballistic range 'TBR') is the horizontal distance between you and the target animal. This is the same whether it be uphill or downhill.

    Couple of images to help explain TBR:
    Name:  Ballist-30_1.jpg
Views: 493
Size:  15.9 KB

    Name:  patentwar01op.png
Views: 807
Size:  30.3 KB

    Best thing to do (if you haven't already) would be to purchase a rangefinder with built in angle compensation and have it set up to display the actual shooting distance (TBR).
    Hunting is not a hobby.....its an addiction

  8. #8
    Member
    Join Date
    Jul 2013
    Location
    Tasman
    Posts
    936
    The OP understands the concept, it's the correction they're after.

    Edit: sorry jumped the gun there Bryan, a TBR range finder coupled with verified drop chart will be a good start.
    Last edited by Moutere; 06-03-2015 at 10:51 AM.

  9. #9
    Member gadgetman's Avatar
    Join Date
    Jan 2012
    Location
    Christchurch
    Posts
    14,891
    As Moutere said, gravity only affects the horizontal component of the projectiles travel. If you are shooting 100m at 45 degrees up or down hill then the horizontal component is cos(45) * 100 = 70.7m, so it has the same drop as a 70m horizontal shot. This is an approximation as the projectile still slows as if it is travelling the 100m plus the extra deceleration of the vertical component of gravity sin(45) * 9.8 ms-2, but these tend to be negligible over the distances we are dealing with.
    There are only three types of people in this world. Those that can count, and those that can't!

  10. #10
    Member
    Join Date
    May 2012
    Location
    Taranaki
    Posts
    1,484
    Minor point but the method based on horizontal distance gets worse the further out you get. It works fine at "normal" hunting distances out to 400 or 500 or so but after that I would recommend you estimate the angle and put that into you ballistic data.

    I would have tried to explain angle shooting as gravity deflection is always the same regardless of angle but with angle some of that deflection is along the line of sight instead of perpendicular to it i.e. vertical. The portion of gravity deflection along the line of sight you don’t see so you are simply left with less vertical deflection. (i.e. what Gadgetman said!)

    Couple of other points though about hold over. As Dougie's data shows, a 300m shot with a 30 degree angle (quite steep) changes your point of impact about 3 inches. Typically this would not result in a clean miss on a good central shoulder shot. The other consideration is the angle you are looking at the animal at. If you are above an animal you want to hit it a little high to angle the projectile through the vitals. If you are below an animal you need to aim a little low on the shoulder for the same reason.

    Lastly @Dougie, I suggest you sight your 223 in at 200m and re-run those deflection numbers. You will see, with a 200m zero, it is quite easy to hold over on animals out to 300m or so at typical 223 velocities.
    veitnamcam and Grunta like this.

  11. #11
    Member
    Join Date
    Dec 2013
    Posts
    603
    Quote Originally Posted by Moutere View Post
    The OP understands the concept, it's the correction they're after.
    Hopefully he still understands it after reading some of the replies ...
    Dougie and BRADS like this.

  12. #12
    A Good Keen Girl Dougie's Avatar
    Join Date
    Jun 2012
    Location
    Hawkes Bay
    Posts
    4,573
    Quote Originally Posted by Gillie View Post
    Lastly @Dougie, I suggest you sight your 223 in at 200m and re-run those deflection numbers. You will see, with a 200m zero, it is quite easy to hold over on animals out to 300m or so at typical 223 velocities.
    But I don't like hold-over, that's the point

    Sorry slightly off topic but one of the reasons I love my .223 so much is that it doesn't lie. It's been a great learning tool for me to have often subtle factors with a big calibre come glaring down at me with the small, light bullet. Wind..doesn't lie. Distance...doesn't lie. I've had great fun learning to dial with my little Weaver scope on this rifle. You'll see the other day when I shot my first deer with it, I dialled! 179 yards, 2.07inches drop, 1.1MOA - I sure did click those four clicks!!!

    (also at 300yards I have only 448fpe and 1914fps so probably not happily hitting bigger deer out there! I like +500fpe)
    JRW87 likes this.
    She loves the free fresh wind in her hair; Life without care. She's broke but it's oke; that's why the lady is a tramp.

    Rule 4: Identify your target beyond all doubt

  13. #13
    Rabbit Herder StrikerNZ's Avatar
    Join Date
    Mar 2012
    Location
    South Canterbury
    Posts
    1,263


    This is listed in metres, but it's perfectly applicable to treat the chart as yards instead.

    A note for the keen - As far as I can process, while you reduce your distance for the vertical component, you should still calculate your wind based on the full distance. Particularly of effect the further out/steeper you go.
    Dougie, DanS and Marty Henry like this.

  14. #14
    Member
    Join Date
    Jan 2015
    Location
    Nelson
    Posts
    961
    Has the Coriolis effect been taken into account
    Dougie, BRADS and Shamus like this.

  15. #15
    Member GravelBen's Avatar
    Join Date
    Aug 2012
    Location
    Gorrre
    Posts
    3,059
    Quote Originally Posted by StrikerNZ View Post
    A note for the keen - As far as I can process, while you reduce your distance for the vertical component, you should still calculate your wind based on the full distance. Particularly of effect the further out/steeper you go.
    That makes sense now that you mention it, though I hadn't thought about it before - the wind is acting on the bullet over its flight time across the full travelled distance.
    Dougie likes this.

 

 

Similar Threads

  1. Angle Cosine Indicator
    By Dead is better in forum Firearms, Optics and Accessories
    Replies: 17
    Last Post: 24-12-2014, 08:45 AM
  2. leica geovid dioptre compensation dials jammed
    By PerazziSC3 in forum Firearms, Optics and Accessories
    Replies: 2
    Last Post: 27-02-2013, 03:03 PM
  3. Ballistic fte update now angle meter not working on HUD
    By Smiddy in forum Reloading and Ballistics
    Replies: 3
    Last Post: 26-01-2013, 11:56 PM
  4. GETTING THE ANGLE RIGHT
    By Scribe in forum Shooting
    Replies: 16
    Last Post: 17-07-2012, 12:04 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
Welcome to NZ Hunting and Shooting Forums! We see you're new here, or arn't logged in. Create an account, and Login for full access including our FREE BUY and SELL section Register NOW!!