Page 4 of 5 FirstFirst ... 2345 LastLast
Results 31 to 40 of 46

Thread: Does shooting position affect Zero?

  1. #31
    Join Date
    Dec 2011
    Location
    Southeastern Wisconsin
    Posts
    45
    Feedback Score
    0
    Artic1, I think you've missed the point being brought up by the OP. In addition to talking about different shooting positions, he was asking about shooting from DIFFERENT ELEVATIONS at the same target (prone on the ground versus on an elevated bench in the OP's description). That would definitely change the "zero", even with your definition.

    Most people who I know think of "zero" in a practical term define it as having "zero error" between point of aim and point of impact at a given distance. That includes considering every variable that gets into the picture - how the weapon was held (lots of variables here, of course), wind effect, the angle of the weapon (shooting uphill or downhill, for example), and all the other variables that come into play.

    Even if one were shooting in a windless tunnel with the weapon bolted down to a non-moving base, there can be changes to the point of impact over time due to variables beyond our control. Thus, "zero" is not a theoretical mathematics exercise of aligning an optical sight to a never-changing trajectory.
    Last edited by SkipD; 12-16-14 at 07:18.

  2. #32
    Join Date
    Nov 2009
    Location
    Norway
    Posts
    1,476
    Feedback Score
    0
    Artic1, I think you've missed the point being brought up by the OP. In addition to talking about different shooting positions, he was asking about shooting from DIFFERENT ELEVATIONS at the same target (prone on the ground versus on an elevated bench in the OP's description). That would definitely change the "zero", even with your definition.
    How so?

    Using the example in the OP, there is negligible movement of the gun required in order to shoot at the same target.

    ETA: The angle difference is 2 degrees, which really does not affect anything.
    Last edited by Arctic1; 12-16-14 at 08:26.
    It's not about surviving, it's about winning!

  3. #33
    Join Date
    Apr 2007
    Location
    FL
    Posts
    9,246
    Feedback Score
    28 (100%)
    Quote Originally Posted by SkipD View Post
    Artic1, I think you've missed the point being brought up by the OP. In addition to talking about different shooting positions, he was asking about shooting from DIFFERENT ELEVATIONS at the same target (prone on the ground versus on an elevated bench in the OP's description). That would definitely change the "zero", even with your definition.
    This did get missed.

    When shooting at an angle, one adjusts for actual horizontal distance for drop, but adjusts for wind by true range.
    One needs to do some basic math with some simple tools to determine angle and the horizontal distance for precise work, or use a laser rangefinder that does it for you (I like the Leupold RX-1200i TBR/DNA).
    For non-precision work, the rule is: hold a low according to angle.

    That said, Arctic1 is right, 5 feet makes no practically measurable difference.
    Jack Leuba
    Director, Military and Government Sales
    Knight's Armament Company
    jleuba@knightarmco.com

  4. #34
    Join Date
    Feb 2013
    Location
    CONUS
    Posts
    5,184
    Feedback Score
    3 (100%)
    Quote Originally Posted by StainlessSlide View Post
    Can anyone give their typical POI shift at a fixed distance, caused by their changing from prone to standing, shooting an M4-like carbine? Obviously there are a million variables (as discussed in the thread), but it would be nice to have an order of magnitude estimate. Is it typically .5 MOA, or 2 MOA, or what?

    Are there shooting disciplines which use different positions while shooting at the same range? If so, does anyone know their position dope (as distinct from range compensation) for a light 5.56 carbine? Or any 5.56?
    I went through my logbook and reviewed my sight settings for shooting a reduced course, all at 100 yards, using the SR-1, SR-21 and MR-31 targets. I have different sight adjustments for each position using 62g reloads traveling at 2700 fps in a 20" bbl AR-15 with match sights. I zero my rifle from the prone position using a sling with no other support and make adjustments when moving to other positions.

    At 100 yards shooting prone, I shoot at my base line prone no wind zero.
    At 100 yards shooting offhand, I have to add 1-1/2 MOA elevation to the prone no wind zero.
    At 100 yards shooting kneeling, I have to add 1/2 MOA elevation and come 1 MOA left windage from my prone no wind zero.
    At 100 yards shooting sitting, I don't have to make an elevation change, but I have to come 1 MOA left windage from my prone no wind zero.

    Lighting changes on the target and sights require different adjustments. Winds at 10 MPH or faster also require adjustments. Changing the sling hole position for the frogs requires elevation adjustments.

    Bear in mind that I am trying to hit a X-Ring that runs from 11/16" on a MR-31 target to 1-5/16" on a SR-1 target.

    I hope this answers your question.
    Last edited by T2C; 12-17-14 at 05:22.
    Train 2 Win

  5. #35
    Join Date
    Sep 2013
    Location
    NE
    Posts
    305
    Feedback Score
    2 (100%)
    Reading all this makes my head want to explode...really. (sinus infection)
    I'm not even sure where to begin - so I'll start with the definition of "Zero"
    The term zero implies that there are “zero” adjustments needed (windage & elevation) on your sights when your point of impact coincides with your point of aim. The distance where your bullet travels can be anything you choose. i.e. the rifle is zero’d for 300 yds.
    There are actually two types of zeros and based on your application, they both have bearing.
    So…Zeroing: What is the definition?
    The average answer that is usually given, is something akin to: “adjusting the sights so that the bullets impact where we are aiming.”
    However in the military, it has a slightly different twist: “Adjusting the rifle sights so bullets hit the aiming point at a given range/distance.”
    Which is right?
    Both answers are correct, a more literal definition and where in fact the word comes from, is where the bullet path and the line of sight intersect and their resulting value in any form of measurement is a “Zero”. So some folks may have multiple zeros on a given rifle and some others my only have one.
    The Army has developed a zeroing process that is used around two different marksmanship techniques, one for known distance and the other for unknown distance.
    With known distances – we have specific zeros for multiple ranges – i.e. 100m, 200m, 300m 500m etc. In simple terms these are repeatable sight settings that will enable bullet impact (POI) and line of sight (POA) to intersect. Common in precision work – SDM’s, Snipers, etc.
    With unknown distances – we use a technique known as BSZ – Battle Sight Zero – this is where the rifle is zeroed at a specific distance that is limited by the trajectory so that any target from that far distance – on in, can be engaged with a center mass shot. At some of these distances the impact may be high and some may be low, but they all fall within an acceptable radius of hits. In simpler terms a rifle that has a proper BSZ will print hits in a 12” circle from 0 m out to 375 m – as long as the POA is center mass. You’ll get a hit on Jimmy Jihad with a center of mass hold – it may induce testicular trauma or it may give him a tracheotomy – but in this application a hit is a hit. We don’t need to be concerned about trying to rapidly adjust our sights – simply hold CM and press the pew switch.
    It is also important to add that in one of the posts, a mention was made of Mechanical Zero – and it was done so, completely out of context. To be sure – Mechanical Zero is the process of mechanically centering your sights so that they have equal amounts of windage and a starting point for elevation. It has NOTHING to do with POI or POA. None. It is merely a starting point from which an actual shooting zero is determined.
    So – the OP’s Question and the body of the text were actually discussing two different things.
    The OP title question was: “Does Shooting Position Affect Zero?” Short answer – Yes. Absolutely.
    More on that later.
    The discussion by the OP is really asking a different question with some serious misconceptions.
    a) A 100yd zero doesn’t produce a flatter path – the trajectory is the trajectory. What he is skirting around is bullet drop – the bullet hasn’t gone far enough to see the effects of gravity.
    b) Changing the height of the barrel from the ground, i.e. going from prone to seated at a bench has nothing to do with increased angle above the horizon or higher parabolic curves.
    c) What the OP is talking about is a Battle Sight Zero – nothing more.
    Now – back to the “does shooting position affect zeros?” Again – absolutely and some astute posts here have hit on exactly why. F2S hit on this perfectly in post #5. When we are discussing duty guns with duty ammo and for the most part – not seriously trained precision shooters – these differences are as he termed “absorbed” in the precision potential – i.e. a shooter / rifle combo that shoots 2-3 MOA from a variety of positions and holds isn’t going to notice a 1-1/2 MOA shift from shooting off a barricade to going prone.
    However when we look at precision work with optics and with good irons – position induced zero changes are not only common, but are to be expected. National Match shooters see this all the time – positions run from 200 yd off hand (standing) to 200 yd rapid sitting with a tight sling, to 300 rapid prone, w/ adifferent setting on the tight sling and 600 yd prone slow with a different sling tension. Each positon had different zeros. Even from the same distance. My 200 Offhand vs 200 Sitting varied by 1-1/4 in elevation and ¾ MOA in windage. I wanted my shots – sometimes without the luxury of sighters centered up. Ammo will produce different zeros, (obviously) Environmental conditions will induce zero changes – meaning my zero was changed at a particular yard line before round one went down the pipe. These changes were required by not only position, but temperature, light, and even particular range facilities. That’s why we keep our DOPE books. I can go back to each yard line / position / range and look at my different zero’s for that particular engagement – set the sights and that first round more often than not was centered up exactly where it was supposed to go.
    Changes in position provide for a change in the shooters head position, cheek weld, eye relief, buttstock position, trigger contact, non-firing hand position etc – all of these variables change the dynamic motion of the rifle – simply, if you hold the rifle differently – it will have different POI. This is why competition shooters strive for consistency and repeatability. These are virtues in precision shooting.
    I can write volumes about this – but the bottom line is that changing positions WILL have an effect on your zero. It is however, vital to understand the context in that a ¾ moa rifle will show these influences far greater than a 3 moa bullet hose.
    Hope this helps.
    Last edited by opsoff1; 12-17-14 at 16:16.
    opsoff

    "I'd rather go down the river with seven studs than with a hundred shitheads"- Colonel Charlie Beckwith

  6. #36
    Join Date
    Nov 2009
    Location
    Norway
    Posts
    1,476
    Feedback Score
    0
    It is also important to add that in one of the posts, a mention was made of Mechanical Zero – and it was done so, completely out of context. To be sure – Mechanical Zero is the process of mechanically centering your sights so that they have equal amounts of windage and a starting point for elevation. It has NOTHING to do with POI or POA. None. It is merely a starting point from which an actually shooting zero is determined.
    I changed my post, as to not cause any confusion. I see that the wording I used was incorrect.

    a) A 100yd zero doesn’t produce a flatter path – the trajectory is the trajectory. What he is skirting around is bullet drop – the bullet hasn’t gone far enough to see the effects of gravity.
    This is not correct at all. Gravity affects the projectile the moment it leaves the muzzle.
    We compensate for gravity when zeroing our rifles by depressing the sight line, so that when aiming at a target with the sight line horizontal, the bore axis is at a slight upwards angle in relation to the sight line.
    If you remove the zero distance, and shoot the gun with the bore axis parallell to a flat surface, the bullet will drop 65mm at 100 meters using my weapon/optic/ammo combo above.

    A 100 meter zero does have a flatter trajectory when compared against a 50/200 or 30/300, in relation to the SIGHT LINE. A 100 meter zero is also unique in that the projectile will not rise above the sight line at any point along the trajectory.
    It's not about surviving, it's about winning!

  7. #37
    Join Date
    Dec 2009
    Location
    Utah
    Posts
    8,422
    Feedback Score
    3 (100%)
    Quote Originally Posted by Arctic1 View Post
    A 100 meter zero does have a flatter trajectory when compared against a 50/200 or 30/300, in relation to the SIGHT LINE...
    Only out to a certain range. Beyond that range, the bullet drop will be greater.

    But the different zeros will not change the actual trajectory. The part of the trajectory that is from 0-100 will have the same parabola whether the rifle is sighted in at 100 meters or 500 meters
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  8. #38
    Join Date
    Nov 2009
    Location
    Norway
    Posts
    1,476
    Feedback Score
    0
    Quote Originally Posted by MistWolf View Post
    Only out to a certain range. Beyond that range, the bullet drop will be greater.

    But the different zeros will not change the actual trajectory. The part of the trajectory that is from 0-100 will have the same parabola whether the rifle is sighted in at 100 meters or 500 meters
    Yes, something I have been saying all along, by referring to zero trajectory - bullet path in relation to sight line. And your reference to the actual parabola extends to infinty, regardless of zero. We do not physically alter the bore axis.

    The bullet drop is slightly greater than a weapon zeroed at 200 and 300. At 600 meters, the numbers are as follows for impact below sight line:

    100m: -3 meters
    200m: -2,7 meters
    300m: -2,3 meters
    It's not about surviving, it's about winning!

  9. #39
    Join Date
    Sep 2013
    Location
    NE
    Posts
    305
    Feedback Score
    2 (100%)
    Quote Originally Posted by Arctic1 View Post
    I changed my post, as to not cause any confusion. I see that the wording I used was incorrect.
    This is not correct at all. Gravity affects the projectile the moment it leaves the muzzle.
    We compensate for gravity when zeroing our rifles by depressing the sight line, so that when aiming at a target with the sight line horizontal, the bore axis is at a slight upwards angle in relation to the sight line.
    If you remove the zero distance, and shoot the gun with the bore axis parallell to a flat surface, the bullet will drop 65mm at 100 meters using my weapon/optic/ammo combo above.

    A 100 meter zero does have a flatter trajectory when compared against a 50/200 or 30/300, in relation to the SIGHT LINE. A 100 meter zero is also unique in that the projectile will not rise above the sight line at any point along the trajectory.
    You contradicted yourself from post #9;
    “The trajectory of a given load shot through a given weapon is the same, regardless of the zero distance.”
    Gravity affects the projectile the moment it leaves the muzzle...It does? Really?
    So - it seems that we need to be super accurate in how this is discussed, so I will offer this:
    We do NOT "compensate for gravity when zeroing our rifles by depressing the sight line" au contraire. And this relates to your comment in the last post – “We do not physically alter the bore axis.” We do – we alter the angle of the bore (axis). What we actually do is elevate muzzle. Launching the bullet at a higher angle does compensate for the effects of gravity. If we depressed our sight line we'd be aiming at the dirt.
    In more precise terms, an increase in the angle of departure to counter the effects of gravity will allow the bullet to reach further distances.

    Also -
    "A 100 meter zero is also unique in that the projectile will not rise above the sight line at any point along the trajectory."
    While true with M4's, M16's other rifles that have sights mounted high above the bore axis, it isn't a universal "truism". Try doing this with a low mount sight on a bolt gun - i.e. an iron sight on a bolt rifle that is 3/4 inch above the bore axis and zeroed at 100yds will print aproximately 1/4 in high at 50 & 75 yds. Just sayin...

    SkipD put it very nicely in post #15
    “I beg to differ. If you do anything with a firearm that changes how the recoil affects the barrel position before the bullet leaves the barrel, you will definitely affect the point of impact relative to the sight picture. For example, if you held the rifle down on a rest for one shot and made another shot holding the rifle offhand, you can expect different points of impact even though the sight settings have not changed. To me, a change in point of impact with no change in sight settings is a change in the "zero".
    He is dead nuts right.

    In the end – what we are discussing is a “ZERO” meaning that a sight setting at a given distance will have the line of sight / point of aim (POA) coincide exactly with point of impact (POI) – meaning that there are zero adjustments required to shoot that distance. Or for those fond of the Cartesian Coordinate Grid aka the X/Y grid - the intersection of X (windage) and Y (elevation) is at zero/zero.

    The entire integrated act of firing a rifle / pistol / pellet gun takes into account the “system” the Rifle/Shooter interface – hold, tension, sight picture, sight alignment, sling, bipod, rest, wind, weather, temp, etc etc. Talk to competitive shooters - we/they have “No Wind Zeros” at every yard line, they have Sitting, Offhand, Kneeling, Prone, Prone Rapid etc zeros for positions. After all aren’t we trying to “hit what we aim at”?
    If I put my 300yd prone, no wind zero on the rifle and lay down - see a quartering wind coming left to right at 10mph, I will adjust off my no wind zero (1/2 value) 1 min, maybe 1-1/4 mins left. I hold center and shoot my round and it goes exactly where it is supposed to go - center. POA. You have to have a zero to start from to shoot at any distance.

    I'm not writing this to be a d*ck - but rather with a bit of tongue in cheek. In all of this discussion it is clear that most of us are talking about the same things - just different ways to skin a cat.

    The OP’s original question; "Does Shooting Position Affect Zero" still remains… and the answer is still a resounding YES.
    opsoff

    "I'd rather go down the river with seven studs than with a hundred shitheads"- Colonel Charlie Beckwith

  10. #40
    Join Date
    Nov 2009
    Location
    Norway
    Posts
    1,476
    Feedback Score
    0
    You are not being a dick, there just seems to be an an issue in either communicating or comprehending the actual point I am trying to make.

    I'll try to summarize.

    1. This is the AR Technical Discussion, so I don't see how the zero trajectory of a different weapon system, like a bolt gun with low sights, is relevant to the discussion.

    2. And I am not contradicting myself, which you would see if you read the entire sentence, ref depressing the sight line.

    We are talking about the zero of a rifle, which we all agree is when you do not need to make any adjustments to have POA/POI at a given distance.

    In this regard, there are two elements that need to be separated

    a. Actual trajectory of the projectile - for a given load fired from a given weapon, the bore axis angle/angle of departure required to hit a specific point at a specific distance, is the same. This does not take the sight line into account. Really not relevant to the discussion.

    b. The "Zero trajectory" - this is the bullet path; near/far zero and max ordinate, in relation to the sight line. This is what is most often talked about, when people discuss the flatness of a trajectory when zeroing their rifle.

    As for my comment on depressing the sight line, you did not include where I said:

    so that when aiming at a target with the sight line horizontal, the bore axis is at a slight upwards angle in relation to the sight line
    When we zero a rifle, we are in fact adjusting the optic/sight line, so that the projectile will intersect the sight line at specific distances we determine, based on our requirements. For longer distance zeros, we elevate the rear sight so that the sight line is slightly depressed compared to the last shots. When we then sight in on the target again, the bore angle is slightly increased. Which is what I said.

    We do not physically adjust the bore axis of the barrel, by taking a tool to it and bending it up or down. The bore axis angle is elevated or depressed according to our sight adjustments.

    And again, I agree that there are many things that will affect your POI, but apart from environmentals (temperature, barometric pressure, humidity) they don't affect your zero. I see your point about making adjustments on sights capable of this, in order to not use horizontal or vertical holds, but then YOU are changing YOUR zero. If the wind subsides, you will no longer be zeroed for the previous conditions, after having made those adjustments.
    DOPE is very handy to have, but if you use a rifle scope with windage/elevation turrets, you are not altering your zero, since you can set the elevation and windage back to your "zero" setting after making adjustments neccessary to make the shot.

    I also see what has been said about different applications. Requirements will differ between a shooter who wants to hit an 8" circle up to a certain distance, and shooters who always aim for the x-ring.
    It's not about surviving, it's about winning!

Page 4 of 5 FirstFirst ... 2345 LastLast

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
  •